Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Carrying Amount
Financial assets
Cash and cash equivalents	$ 150,861	$ 193,253
Investment securities, available-for-sale	2,604,625	2,610,760
Investment securities, held-to-maturity	691,663	702,072
Loans held for sale	40,484	56,514
Loans receivable, net of ALLL	5,067,122	4,948,984
Accrued interest receivable	47,363	44,524
Non-marketable equity securities	24,199	27,495
Total financial assets	8,626,317	8,583,602
Financial liabilities
Deposits	7,016,194	6,945,008
FHLB advances	313,969	394,131
Repurchase agreements and other borrowed funds	452,593	430,016
Subordinated debentures	125,884	125,848
Accrued interest payable	3,608	3,517
Interest rate swaps	27,598	19,499
Total financial liabilities	7,939,846	7,918,019
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	150,861	193,253
Investment securities, available-for-sale	0	0
Investment securities, held-to-maturity	0	0
Loans held for sale	40,484	56,514
Loans receivable, net of ALLL	0	0
Accrued interest receivable	47,363	44,524
Non-marketable equity securities	0	0
Total financial assets	238,708	294,291
Financial liabilities
Deposits	5,626,969	5,654,638
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Accrued interest payable	3,608	3,517
Interest rate swaps	0	0
Total financial liabilities	5,630,577	5,658,155
Estimated Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Investment securities, available-for-sale	2,604,625	2,610,760
Investment securities, held-to-maturity	720,190	729,513
Loans held for sale	0	0
Loans receivable, net of ALLL	4,897,887	4,851,934
Accrued interest receivable	0	0
Non-marketable equity securities	24,199	27,495
Total financial assets	8,246,901	8,219,702
Financial liabilities
Deposits	1,389,225	1,293,506
FHLB advances	324,946	401,530
Repurchase agreements and other borrowed funds	452,593	430,016
Subordinated debentures	81,174	81,840
Accrued interest payable	0	0
Interest rate swaps	27,598	19,499
Total financial liabilities	2,275,536	2,226,391
Estimated Fair Value | Level 3
Financial assets
Cash and cash equivalents	0	0
Investment securities, available-for-sale	0	0
Investment securities, held-to-maturity	0	0
Loans held for sale	0	0
Loans receivable, net of ALLL	132,426	132,649
Accrued interest receivable	0	0
Non-marketable equity securities	0	0
Total financial assets	132,426	132,649
Financial liabilities
Deposits	0	0
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Accrued interest payable	0	0
Interest rate swaps	0	0
Total financial liabilities	$ 0	$ 0