Carrying Amount and Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Carrying Amount
Financial Assets
Cash and Cash Equivalents	$ 442,409	$ 155,657
Investment securities, available-for-sale	2,387,428	3,222,829
Investment securities, held-to-maturity	520,997
Loans Held-for-sale	46,726	46,738
Loans Receivable, net of ALLL	4,358,342	3,932,487
Accrued interest receivable	40,587	41,898
Non-marketable Equity Securities	52,868	52,192
Interest rate swaps		1,896
Total Financial Assets	7,849,357	7,453,697
Financial Liabilities
Deposits	6,345,212	5,579,967
FHLB advances	296,944	840,182
Repurchase agreements and other borrowed funds	404,418	321,781
Subordinated debentures	125,705	125,562
Accrued interest payable	4,155	3,505
Interest rate swaps	16,668
Total financial liabilities	7,193,102	6,870,997
Estimated Fair Value | Level 1
Financial Assets
Cash and Cash Equivalents	442,409	155,657
Investment securities, available-for-sale	0	0
Investment securities, held-to-maturity	0
Loans Held-for-sale	46,726	46,738
Loans Receivable, net of ALLL	0	0
Accrued interest receivable	40,587	41,898
Non-marketable Equity Securities	0	0
Interest rate swaps		0
Total Financial Assets	529,722	244,293
Financial Liabilities
Deposits	4,928,771	4,258,213
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Accrued interest payable	4,155	3,505
Interest rate swaps	0
Total financial liabilities	4,932,926	4,261,718
Estimated Fair Value | Level 2
Financial Assets
Cash and Cash Equivalents	0	0
Investment securities, available-for-sale	2,387,428	3,222,829
Investment securities, held-to-maturity	550,946
Loans Held-for-sale	0	0
Loans Receivable, net of ALLL	4,288,417	3,807,993
Accrued interest receivable	0	0
Non-marketable Equity Securities	52,868	52,192
Interest rate swaps		1,896
Total Financial Assets	7,279,659	7,084,910
Financial Liabilities
Deposits	1,421,234	1,341,382
FHLB advances	312,363	857,551
Repurchase agreements and other borrowed funds	404,418	321,781
Subordinated debentures	76,711	71,501
Accrued interest payable	0	0
Interest rate swaps	16,668
Total financial liabilities	2,231,394	2,592,215
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
Loans Held-for-sale	0	0
Loans Receivable, net of ALLL	149,769	187,731
Accrued interest receivable	0	0
Non-marketable Equity Securities	0	0
Interest rate swaps		0
Total Financial Assets	149,769	187,731
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
Total financial liabilities	$ 0	$ 0