Loans and Allowance for Loan Losses - Risk category of loans by class of loans (Details 10) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Risk category of loans by class of loans
Total loans	$ 4,189,368	$ 4,175,008	$ 4,119,235
Loans Receivable
Risk category of loans by class of loans
Total loans	4,189,368	4,175,008	4,119,235
Loans Receivable | Pass
Risk category of loans by class of loans
Total loans	3,853,017	3,640,803	3,509,262
Loans Receivable | Watch
Risk category of loans by class of loans
Total loans	131,243	161,428	170,211
Loans Receivable | Performing Substandard
Risk category of loans by class of loans
Total loans	176,332	261,941	323,644
Loans Receivable | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	27,864	109,894	115,340
Loans Receivable | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Not Rated
Risk category of loans by class of loans
Total loans	912	942	778
Loans Receivable | Residential mortgage
Risk category of loans by class of loans
Total loans	1,278,559	1,214,203	1,128,336
Loans Receivable | Residential mortgage | Pass
Risk category of loans by class of loans
Total loans	1,185,658	1,102,746	999,323
Loans Receivable | Residential mortgage | Watch
Risk category of loans by class of loans
Total loans	27,341	33,689	39,105
Loans Receivable | Residential mortgage | Performing Substandard
Risk category of loans by class of loans
Total loans	51,222	65,179	73,277
Loans Receivable | Residential mortgage | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	14,338	12,589	16,631
Loans Receivable | Residential mortgage | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Residential mortgage | Not Rated
Risk category of loans by class of loans
Total loans
Loans Receivable | Residential construction
Risk category of loans by class of loans
Total loans	331,681	381,677	408,966
Loans Receivable | Residential construction | Pass
Risk category of loans by class of loans
Total loans	292,116	292,264	290,804
Loans Receivable | Residential construction | Watch
Risk category of loans by class of loans
Total loans	18,096	32,907	47,182
Loans Receivable | Residential construction | Performing Substandard
Risk category of loans by class of loans
Total loans	16,631	37,804	45,450
Loans Receivable | Residential construction | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	4,838	18,702	25,530
Loans Receivable | Residential construction | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Residential construction | Not Rated
Risk category of loans by class of loans
Total loans
Loans Receivable | Consumer installment
Risk category of loans by class of loans
Total loans	261,433	152,748	125,896
Loans Receivable | Consumer installment | Pass
Risk category of loans by class of loans
Total loans	257,563	147,214	121,166
Loans Receivable | Consumer installment | Watch
Risk category of loans by class of loans
Total loans	966	1,086	1,117
Loans Receivable | Consumer installment | Performing Substandard
Risk category of loans by class of loans
Total loans	2,505	3,653	2,706
Loans Receivable | Consumer installment | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	399	795	907
Loans Receivable | Consumer installment | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Consumer installment | Not Rated
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial
Risk category of loans by class of loans
Total loans	2,317,695	2,426,380	2,456,037
Loans Receivable | Commercial | Pass
Risk category of loans by class of loans
Total loans	2,117,680	2,098,579	2,097,969
Loans Receivable | Commercial | Watch
Risk category of loans by class of loans
Total loans	84,840	93,746	82,807
Loans Receivable | Commercial | Performing Substandard
Risk category of loans by class of loans
Total loans	105,974	155,305	202,211
Loans Receivable | Commercial | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	8,289	77,808	72,272
Loans Receivable | Commercial | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial | Not Rated
Risk category of loans by class of loans
Total loans	912	942	778
Loans Receivable | Commercial | Commercial (secured by real estate)
Risk category of loans by class of loans
Total loans	1,748,145	1,813,365	1,836,477
Loans Receivable | Commercial | Commercial (secured by real estate) | Pass
Risk category of loans by class of loans
Total loans	1,595,141	1,592,677	1,596,876
Loans Receivable | Commercial | Commercial (secured by real estate) | Watch
Risk category of loans by class of loans
Total loans	67,017	80,997	72,067
Loans Receivable | Commercial | Commercial (secured by real estate) | Performing Substandard
Risk category of loans by class of loans
Total loans	78,750	117,543	148,419
Loans Receivable | Commercial | Commercial (secured by real estate) | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	7,237	22,148	19,115
Loans Receivable | Commercial | Commercial (secured by real estate) | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial | Commercial (secured by real estate) | Not Rated
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial | Commercial & industrial
Risk category of loans by class of loans
Total loans	436,988	458,246	450,222
Loans Receivable | Commercial | Commercial & industrial | Pass
Risk category of loans by class of loans
Total loans	418,354	401,606	393,894
Loans Receivable | Commercial | Commercial & industrial | Watch
Risk category of loans by class of loans
Total loans	5,716	5,404	4,652
Loans Receivable | Commercial | Commercial & industrial | Performing Substandard
Risk category of loans by class of loans
Total loans	11,458	18,477	15,916
Loans Receivable | Commercial | Commercial & industrial | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	548	31,817	34,982
Loans Receivable | Commercial | Commercial & industrial | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial | Commercial & industrial | Not Rated
Risk category of loans by class of loans
Total loans	912	942	778
Loans Receivable | Commercial | Commercial construction
Risk category of loans by class of loans
Total loans	132,562	154,769	169,338
Loans Receivable | Commercial | Commercial construction | Pass
Risk category of loans by class of loans
Total loans	104,185	104,296	107,199
Loans Receivable | Commercial | Commercial construction | Watch
Risk category of loans by class of loans
Total loans	12,107	7,345	6,088
Loans Receivable | Commercial | Commercial construction | Performing Substandard
Risk category of loans by class of loans
Total loans	15,766	19,285	37,876
Loans Receivable | Commercial | Commercial construction | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	504	23,843	18,175
Loans Receivable | Commercial | Commercial construction | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial | Commercial construction | Not Rated
Risk category of loans by class of loans
Total loans