Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Carrying Amount
Financial assets
Cash and cash equivalents	$ 242,835	$ 442,409
Investment securities, available-for-sale	2,530,994	2,387,428
Investment securities, held-to-maturity	651,822	520,997
Loans held for sale	40,456	46,726
Loans receivable, net of ALLL	4,745,651	4,358,342
Accrued interest receivable	46,786	40,587
Non-marketable equity securities	24,905	52,868
Total financial assets	8,283,449	7,849,357
Financial liabilities
Deposits	6,673,179	6,345,212
FHLB advances	329,299	296,944
Repurchase agreements and other borrowed funds	447,660	404,418
Subordinated debentures	125,812	125,705
Accrued interest payable	3,641	4,155
Interest rate swaps	23,623	16,668
Total financial liabilities	7,603,214	7,193,102
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	242,835	442,409
Investment securities, available-for-sale	0	0
Investment securities, held-to-maturity	0	0
Loans held for sale	40,456	46,726
Loans receivable, net of ALLL	0	0
Accrued interest receivable	46,786	40,587
Non-marketable equity securities	0	0
Total financial assets	330,077	529,722
Financial liabilities
Deposits	5,388,835	4,928,771
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Accrued interest payable	3,641	4,155
Interest rate swaps	0	0
Total financial liabilities	5,392,476	4,932,926
Estimated Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Investment securities, available-for-sale	2,530,994	2,387,428
Investment securities, held-to-maturity	672,395	550,946
Loans held for sale	0	0
Loans receivable, net of ALLL	4,661,095	4,288,417
Accrued interest receivable	0	0
Non-marketable equity securities	24,905	52,868
Total financial assets	7,889,389	7,279,659
Financial liabilities
Deposits	1,287,943	1,421,234
FHLB advances	340,776	312,363
Repurchase agreements and other borrowed funds	447,660	404,418
Subordinated debentures	78,002	76,711
Accrued interest payable	0	0
Interest rate swaps	23,623	16,668
Total financial liabilities	2,178,004	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	138,742	149,769
Accrued interest receivable	0	0
Non-marketable equity securities	0	0
Total financial assets	138,742	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