| Summary of fair values for assets and liabilities recorded at fair value | 
        
 A summary of fair values for assets and liabilities recorded at fair value consisted of the following: 
  
| (Dollars in Thousands) | 
  | 
Level 1 Inputs | 
  | 
Level 2 Inputs | 
  | 
Level 3 Inputs | 
  | 
Total Fair Value | 
 
| March 31, 2013 | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| ASSETS: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| Securities available for sale: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
|    U.S. Treasury | 
  | 
$ | 
94,905 | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
94,905 | 
  | 
 
|    U.S. Government Agency | 
  | 
  | 
— | 
  | 
  | 
  | 
52,372 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
52,372 | 
  | 
 
|    States and Political Subdivisions | 
  | 
  | 
— | 
  | 
  | 
  | 
82,994 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
82,994 | 
  | 
 
|    Mortgage-Backed Securities | 
  | 
  | 
— | 
  | 
  | 
  | 
67,017 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
67,017 | 
  | 
 
|    Other Securities | 
  | 
  | 
— | 
  | 
  | 
  | 
10,214 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
10,214 | 
  | 
 
|   | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| December 31, 2012 | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| Securities available for sale: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
|    U.S. Treasury | 
  | 
$ | 
97,249 | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
97,249 | 
  | 
 
|    U.S. Government Agency | 
  | 
  | 
— | 
  | 
  | 
  | 
51,664 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
51,664 | 
  | 
 
|    State and Political Subdivisions | 
  | 
  | 
— | 
  | 
  | 
  | 
79,879 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
79,879 | 
  | 
 
|    Mortgage-Backed Securities | 
  | 
  | 
— | 
  | 
  | 
  | 
56,982 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
56,982 | 
  | 
 
|    Other Securities | 
  | 
  | 
— | 
  | 
  | 
  | 
11,211 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
11,211 | 
  | 
 
 
 | 
      
      
        | Summary of estimated fair values of significant financial instruments | 
        
 A summary of estimated fair values of significant financial instruments consisted of the following: 
  
|   | 
  | 
March 31, 2013 | 
 
| (Dollars in Thousands) | 
  | 
Carrying 
Value | 
  | 
Level 1 Inputs | 
  | 
Level 2 Inputs | 
  | 
Level 3 Inputs | 
 
| ASSETS: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| Cash | 
  | 
$ | 
52,677 | 
  | 
  | 
$ | 
52,677 | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
— | 
  | 
 
| Short-Term Investments | 
  | 
  | 
461,714 | 
  | 
  | 
  | 
461,714 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
— | 
  | 
 
| Investment Securities | 
  | 
  | 
307,502 | 
  | 
  | 
  | 
94,905 | 
  | 
  | 
  | 
212,597 | 
  | 
  | 
  | 
— | 
  | 
 
| Loans Held for Sale | 
  | 
  | 
11,422 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
11,422 | 
  | 
  | 
  | 
— | 
  | 
 
| Loans, Net of Allowance for Loan Losses | 
  | 
  | 
1,427,096 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
1,322,918 | 
  | 
 
|   | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| LIABILITIES: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| Deposits | 
  | 
$ | 
2,113,982 | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
2,114,482 | 
  | 
  | 
$ | 
— | 
  | 
 
| Short-Term Borrowings | 
  | 
  | 
50,682 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
50,504 | 
  | 
  | 
  | 
— | 
  | 
 
| Subordinated Notes Payable | 
  | 
  | 
62,887 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
62,889 | 
  | 
  | 
  | 
— | 
  | 
 
| Long-Term Borrowings | 
  | 
  | 
41,224 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
43,962 | 
  | 
  | 
  | 
— | 
  | 
 
 
  
|   | 
  | 
December 31, 2012 | 
 
| (Dollars in Thousands) | 
  | 
Carrying 
Value | 
  | 
Level 1 Inputs | 
  | 
Level 2 Inputs | 
  | 
Level 3 Inputs | 
 
| ASSETS: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| Cash | 
  | 
$ | 
66,238 | 
  | 
  | 
$ | 
66,238 | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
— | 
  | 
 
| Short-Term Investments | 
  | 
  | 
443,494 | 
  | 
  | 
  | 
443,494 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
— | 
  | 
 
| Investment Securities | 
  | 
  | 
296,985 | 
  | 
  | 
  | 
97,249 | 
  | 
  | 
  | 
199,736 | 
  | 
  | 
  | 
— | 
  | 
 
| Loans Held for Sale | 
  | 
  | 
14,189 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
14,189 | 
  | 
  | 
  | 
— | 
  | 
 
| Loans, Net of Allowance for Loan Losses | 
  | 
  | 
1,477,946 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
1,370,056 | 
  | 
 
|   | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| LIABILITIES: | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
  | 
 
| Deposits | 
  | 
$ | 
2,144,996 | 
  | 
  | 
$ | 
— | 
  | 
  | 
$ | 
2,145,547 | 
  | 
  | 
$ | 
— | 
  | 
 
| Short-Term Borrowings | 
  | 
  | 
47,435 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
46,503 | 
  | 
  | 
  | 
— | 
  | 
 
| Subordinated Notes Payable | 
  | 
  | 
62,887 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
62,896 | 
  | 
  | 
  | 
— | 
  | 
 
| Long-Term Borrowings | 
  | 
  | 
46,859 | 
  | 
  | 
  | 
— | 
  | 
  | 
  | 
50,003 | 
  | 
  | 
  | 
— | 
  | 
 
 
 |