Carrying Amount and Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Carrying Amount
Financial assets
Cash and cash equivalents	$ 161,691	$ 155,657
Investment securities, available-for-sale	2,669,180	3,222,829
Investment securities, held-to-maturity	481,476
Loans held for sale	36,133	46,738
Loans receivable, net of ALLL	3,957,900	3,932,487
Accrued interest receivable	41,274	41,898
Non-marketable equity securities	52,192	52,192
Interest rate swaps		1,896
Total financial assets	7,399,846	7,453,697
Financial liabilities
Deposits	5,624,465	5,579,967
FHLB advances	686,744	840,182
Repurchase agreements and other borrowed funds	335,391	321,781
Subordinated debentures	125,597	125,562
Accrued interest payable	3,173	3,505
Interest rate swaps	3,583
Total financial liabilities	6,778,953	6,870,997
Estimated Fair Value | Level 1
Financial assets
Cash and cash equivalents	161,691	155,657
Investment securities, available-for-sale	0	0
Investment securities, held-to-maturity	0
Loans held for sale	36,133	46,738
Loans receivable, net of ALLL	0	0
Accrued interest receivable	41,274	41,898
Non-marketable equity securities	0	0
Interest rate swaps		0
Total financial assets	239,098	244,293
Financial liabilities
Deposits	4,315,105	4,258,213
FHLB advances	0	0
Repurchase agreements and other borrowed funds	0	0
Subordinated debentures	0	0
Accrued interest payable	3,173	3,505
Interest rate swaps	0
Total financial liabilities	4,318,278	4,261,718
Estimated Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Investment securities, available-for-sale	2,669,180	3,222,829
Investment securities, held-to-maturity	498,902
Loans held for sale	0	0
Loans receivable, net of ALLL	3,840,131	3,807,993
Accrued interest receivable	0	0
Non-marketable equity securities	52,192	52,192
Interest rate swaps		1,896
Total financial assets	7,060,405	7,084,910
Financial liabilities
Deposits	1,314,661	1,341,382
FHLB advances	703,287	857,551
Repurchase agreements and other borrowed funds	335,391	321,781
Subordinated debentures	68,673	71,501
Accrued interest payable	0	0
Interest rate swaps	3,583
Total financial liabilities	2,425,595	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	181,948	187,731
Accrued interest receivable	0	0
Non-marketable equity securities	0	0
Interest rate swaps		0
Total financial assets	181,948	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