Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Carrying Amount
Financial assets
Cash and cash equivalents	$ 355,719	$ 442,409
Investment securities, available-for-sale	2,361,830	2,387,428
Investment securities, held-to-maturity	593,314	520,997
Loans held for sale	53,201	46,726
Loans receivable, net of ALLL	4,676,912	4,358,342
Accrued interest receivable	44,563	40,587
Non-marketable equity securities	24,914	52,868
Total financial assets	8,110,453	7,849,357
Financial liabilities
Deposits	6,558,657	6,345,212
FHLB advances	329,470	296,944
Repurchase agreements and other borrowed funds	415,600	404,418
Subordinated debentures	125,776	125,705
Accrued interest payable	3,790	4,155
Interest rate swaps	16,256	16,668
Total financial liabilities	7,449,549	7,193,102
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	355,719	442,409
Investment securities, available-for-sale	0	0
Investment securities, held-to-maturity	0	0
Loans held for sale	53,201	46,726
Loans receivable, net of ALLL	0	0
Accrued interest receivable	44,563	40,587
Non-marketable equity securities	0	0
Total financial assets	453,483	529,722
Financial liabilities
Deposits	5,215,156	4,928,771
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Accrued interest payable	3,790	4,155
Interest rate swaps	0	0
Total financial liabilities	5,218,946	4,932,926
Estimated Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Investment securities, available-for-sale	2,361,830	2,387,428
Investment securities, held-to-maturity	608,781	550,946
Loans held for sale	0	0
Loans receivable, net of ALLL	4,608,899	4,288,417
Accrued interest receivable	0	0
Non-marketable equity securities	24,914	52,868
Total financial assets	7,604,424	7,279,659
Financial liabilities
Deposits	1,347,635	1,421,234
FHLB advances	339,179	312,363
Repurchase agreements and other borrowed funds	415,600	404,418
Subordinated debentures	78,442	76,711
Accrued interest payable	0	0
Interest rate swaps	16,256	16,668
Total financial liabilities	2,197,112	2,231,394
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	144,478	149,769
Accrued interest receivable	0	0
Non-marketable equity securities	0	0
Total financial assets	144,478	149,769
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