Disclosures About Fair Value of Financial Instruments (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Disclosures About Fair Value of Financial Instruments
Significant unrealized appreciation or depreciation in financial instruments	$ 0	$ 0
Financial assets:
Securities available-for-sale	1,016,767,000	1,079,074,000
Securities held-to-maturity	124,061,000	161,969,000
Accrued interest receivable	21,821,000	23,313,000
Financial liabilities:
Borrowed funds	881,645,000	860,047,000
Junior subordinated debentures	103,094,000	103,094,000
Assets transferred between Level 1 and Level 2	0	0
Liabilities transferred between Level 1 and Level 2	0	0
Level 1
Financial assets:
Cash and cash equivalents	391,905,000	451,704,000
Securities available-for-sale	9,850,000	19,304,000
Loans receivable, net	221,000	15,441,000
Accrued interest receivable	21,821,000	23,313,000
Total financial assets	423,797,000	509,762,000
Financial liabilities:
Savings and checking accounts	4,001,482,000	3,878,511,000
Borrowed funds	156,198,000	164,531,000
Accrued interest payable	888,000	888,000
Total financial liabilities	4,158,568,000	4,043,930,000
Level 2
Financial assets:
Securities available-for-sale	994,666,000	1,048,651,000
Securities held-to-maturity	124,061,000	161,969,000
Total financial assets	1,118,727,000	1,210,620,000
Financial liabilities:
Cash flow hedges - swaps	8,037,000	12,932,000
Total financial liabilities	8,037,000	12,932,000
Level 3
Financial assets:
Securities available-for-sale	12,251,000	11,119,000
Loans receivable, net	6,026,490,000	5,937,247,000
Total financial assets	6,038,741,000	5,948,366,000
Financial liabilities:
Time deposits	1,699,937,000	1,927,844,000
Borrowed funds	740,210,000	770,853,000
Junior subordinated debentures	111,220,000	116,066,000
Total financial liabilities	2,551,367,000	2,814,763,000
Carrying amount
Financial assets:
Cash and cash equivalents	391,905,000	451,704,000
Securities available-for-sale	1,016,767,000	1,079,074,000
Securities held-to-maturity	121,366,000	155,081,000
Loans receivable, net	5,734,943,000	5,629,261,000
Accrued interest receivable	21,821,000	23,313,000
FHLB Stock	43,715,000	46,834,000
Total financial assets	7,330,517,000	7,385,267,000
Financial liabilities:
Savings and checking accounts	4,001,482,000	3,878,511,000
Time deposits	1,667,397,000	1,886,089,000
Borrowed funds	881,645,000	860,047,000
Junior subordinated debentures	103,094,000	103,094,000
Cash flow hedges - swaps	8,037,000	12,932,000
Accrued interest payable	888,000	888,000
Total financial liabilities	6,662,543,000	6,741,561,000
Estimated fair value
Financial assets:
Cash and cash equivalents	391,905,000	451,704,000
Securities available-for-sale	1,016,767,000	1,079,074,000
Securities held-to-maturity	124,061,000	161,969,000
Loans receivable, net	6,026,711,000	5,952,688,000
Accrued interest receivable	21,821,000	23,313,000
FHLB Stock	43,715,000	46,834,000
Total financial assets	7,624,980,000	7,715,582,000
Financial liabilities:
Savings and checking accounts	4,001,482,000	3,878,511,000
Time deposits	1,699,937,000	1,927,844,000
Borrowed funds	896,408,000	935,384,000
Junior subordinated debentures	111,220,000	116,066,000
Cash flow hedges - swaps	8,037,000	12,932,000
Accrued interest payable	888,000	888,000
Total financial liabilities	$ 6,717,972,000	$ 6,871,625,000