Loans and Allowance for Loan Losses - Risk category of loans by class of loans (Details 8) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Risk category of loans by class of loans
Total loans	$ 4,193,560	$ 4,175,008	$ 4,127,566
Loans Receivable
Risk category of loans by class of loans
Total loans	4,193,560	4,175,008	4,127,566
Loans Receivable | Pass
Risk category of loans by class of loans
Total loans	3,690,824	3,640,803	3,468,554
Loans Receivable | Watch
Risk category of loans by class of loans
Total loans	134,288	161,428	211,634
Loans Receivable | Performing Substandard
Risk category of loans by class of loans
Total loans	271,681	261,941	316,933
Loans Receivable | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	96,006	109,894	129,704
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	761	942	741
Loans Receivable | Residential mortgage
Risk category of loans by class of loans
Total loans		1,214,203	1,131,248
Loans Receivable | Residential mortgage | Pass
Risk category of loans by class of loans
Total loans	1,139,249	1,102,746	995,981
Loans Receivable | Residential mortgage | Watch
Risk category of loans by class of loans
Total loans	30,806	33,689	40,790
Loans Receivable | Residential mortgage | Performing Substandard
Risk category of loans by class of loans
Total loans	64,103	65,179	75,736
Loans Receivable | Residential mortgage | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	11,817	12,589	18,741
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		381,677	435,375
Loans Receivable | Residential construction | Pass
Risk category of loans by class of loans
Total loans	296,029	292,264	298,592
Loans Receivable | Residential construction | Watch
Risk category of loans by class of loans
Total loans	23,230	32,907	48,168
Loans Receivable | Residential construction | Performing Substandard
Risk category of loans by class of loans
Total loans	37,882	37,804	64,274
Loans Receivable | Residential construction | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	14,592	18,702	24,341
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		152,748	111,118
Loans Receivable | Consumer installment | Pass
Risk category of loans by class of loans
Total loans	161,577	147,214	106,124
Loans Receivable | Consumer installment | Watch
Risk category of loans by class of loans
Total loans	888	1,086	1,476
Loans Receivable | Consumer installment | Performing Substandard
Risk category of loans by class of loans
Total loans	2,794	3,653	2,610
Loans Receivable | Consumer installment | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	389	795	908
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 Portfolio Segment
Risk category of loans by class of loans
Total loans	2,410,204	2,426,380	2,449,825
Loans Receivable | Commercial Portfolio Segment | Pass
Risk category of loans by class of loans
Total loans	2,093,969	2,098,579	2,067,857
Loans Receivable | Commercial Portfolio Segment | Watch
Risk category of loans by class of loans
Total loans	79,364	93,746	121,200
Loans Receivable | Commercial Portfolio Segment | Performing Substandard
Risk category of loans by class of loans
Total loans	166,902	155,305	174,313
Loans Receivable | Commercial Portfolio Segment | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	69,208	77,808	85,714
Loans Receivable | Commercial Portfolio Segment | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial Portfolio Segment | Not Rated
Risk category of loans by class of loans
Total loans	761	942	741
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate)
Risk category of loans by class of loans
Total loans		1,813,365	1,843,207
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate) | Pass
Risk category of loans by class of loans
Total loans	1,593,193	1,592,677	1,586,934
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate) | Watch
Risk category of loans by class of loans
Total loans	65,413	80,997	96,352
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate) | Performing Substandard
Risk category of loans by class of loans
Total loans	128,120	117,543	133,840
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate) | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	17,304	22,148	26,081
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate) | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial Portfolio Segment | Commercial (secured by real estate) | Not Rated
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial
Risk category of loans by class of loans
Total loans		458,246	439,496
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial | Pass
Risk category of loans by class of loans
Total loans	396,363	401,606	381,098
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial | Watch
Risk category of loans by class of loans
Total loans	6,775	5,404	4,126
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial | Performing Substandard
Risk category of loans by class of loans
Total loans	20,320	18,477	17,217
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	29,545	31,817	36,314
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial Portfolio Segment | Commercial & industrial | Not Rated
Risk category of loans by class of loans
Total loans	761	942	741
Loans Receivable | Commercial Portfolio Segment | Commercial construction
Risk category of loans by class of loans
Total loans		154,769	167,122
Loans Receivable | Commercial Portfolio Segment | Commercial construction | Pass
Risk category of loans by class of loans
Total loans	104,413	104,296	99,825
Loans Receivable | Commercial Portfolio Segment | Commercial construction | Watch
Risk category of loans by class of loans
Total loans	7,176	7,345	20,722
Loans Receivable | Commercial Portfolio Segment | Commercial construction | Performing Substandard
Risk category of loans by class of loans
Total loans	18,462	19,285	23,256
Loans Receivable | Commercial Portfolio Segment | Commercial construction | Nonaccrual Substandard
Risk category of loans by class of loans
Total loans	22,359	23,843	23,319
Loans Receivable | Commercial Portfolio Segment | Commercial construction | Doubtful / Loss
Risk category of loans by class of loans
Total loans
Loans Receivable | Commercial Portfolio Segment | Commercial construction | Not Rated
Risk category of loans by class of loans
Total loans