Investment Securities (Details 4) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Available-for-sale securities
Fair Value, Less than 12 months	$ 835,779,000	$ 379,275,000	$ 835,779,000	$ 379,275,000	$ 1,464,928,000
Estimated Unrealized Loss, Less than 12 months	5,756,000	2,949,000	5,756,000	2,949,000	19,187,000
Fair Value, 12 months or greater	59,570,000	146,470,000	59,570,000	146,470,000	76,678,000
Estimated Unrealized Loss, 12 months or greater	15,380,000	25,253,000	15,380,000	25,253,000	18,662,000
Fair Value, Total	895,349,000	525,745,000	895,349,000	525,745,000	1,541,606,000
Estimated Unrealized Loss, Total	21,136,000	28,202,000	21,136,000	28,202,000	37,849,000
Fair value of total securities available-for-sale	6,348,055,000	4,761,143,000	6,348,055,000	4,761,143,000	5,720,675,000
Temporarily impaired securities	884,500,000	473,400,000	884,500,000	473,400,000	1,510,000,000
Fair value securities, having non-credit impairment recognized in AOCI	10,800,000	52,300,000	10,800,000	52,300,000	27,400,000
Impairment losses recognized in earnings on other-than-temporarily impaired securities	294,000	506,000	458,000	1,509,000
U.S. Treasury
Available-for-sale securities
Fair Value, Less than 12 months		4,029,000		4,029,000	5,028,000
Estimated Unrealized Loss, Less than 12 months		1,000		1,000	4,000
Fair Value, Total		4,029,000		4,029,000	5,028,000
Estimated Unrealized Loss, Total		1,000		1,000	4,000
Fair value of total securities available-for-sale	13,076,000	19,145,000	13,076,000	19,145,000	14,113,000
Number of securities in the unrealized loss position		1		1	1
Federal agency - Debt
Available-for-sale securities
Fair Value, Less than 12 months	334,928,000	50,516,000	334,928,000	50,516,000	561,205,000
Estimated Unrealized Loss, Less than 12 months	881,000	289,000	881,000	289,000	5,221,000
Fair Value, Total	334,928,000	50,516,000	334,928,000	50,516,000	561,205,000
Estimated Unrealized Loss, Total	881,000	289,000	881,000	289,000	5,221,000
Fair value of total securities available-for-sale	1,847,232,000	1,090,846,000	1,847,232,000	1,090,846,000	1,142,328,000
Number of securities in the unrealized loss position	13	1	13	1	22
Federal agency - MBS
Available-for-sale securities
Fair Value, Less than 12 months	94,035,000		94,035,000		109,381,000
Estimated Unrealized Loss, Less than 12 months	1,656,000		1,656,000		2,801,000
Fair Value, Total	94,035,000		94,035,000		109,381,000
Estimated Unrealized Loss, Total	1,656,000		1,656,000		2,801,000
Fair value of total securities available-for-sale	534,726,000	466,713,000	534,726,000	466,713,000	551,346,000
Number of securities in the unrealized loss position	7		7		7
CMOs - Federal agency
Available-for-sale securities
Fair Value, Less than 12 months	384,986,000	293,008,000	384,986,000	293,008,000	755,751,000
Estimated Unrealized Loss, Less than 12 months	2,791,000	2,116,000	2,791,000	2,116,000	10,585,000
Fair Value, Total	384,986,000	293,008,000	384,986,000	293,008,000	755,751,000
Estimated Unrealized Loss, Total	2,791,000	2,116,000	2,791,000	2,116,000	10,585,000
Fair value of total securities available-for-sale	3,453,901,000	2,528,237,000	3,453,901,000	2,528,237,000	3,497,147,000
Number of securities in the unrealized loss position	19	16	19	16	30
CMOs - Non-agency
Available-for-sale securities
Fair Value, Less than 12 months	10,142,000	24,327,000	10,142,000	24,327,000	7,718,000
Estimated Unrealized Loss, Less than 12 months	224,000	455,000	224,000	455,000	18,000
Fair Value, 12 months or greater	43,089,000	124,892,000	43,089,000	124,892,000	61,571,000
Estimated Unrealized Loss, 12 months or greater	7,880,000	18,550,000	7,880,000	18,550,000	9,653,000
Fair Value, Total	53,231,000	149,219,000	53,231,000	149,219,000	69,289,000
Estimated Unrealized Loss, Total	8,104,000	19,005,000	8,104,000	19,005,000	9,671,000
Fair value of total securities available-for-sale	91,083,000	217,078,000	91,083,000	217,078,000	118,295,000
Number of securities in the unrealized loss position	10	21	10	21	12
Impairment losses recognized in earnings on other-than-temporarily impaired securities	294,000	212,000	458,000	1,215,000
State and municipal
Available-for-sale securities
Fair Value, Less than 12 months	11,688,000	2,810,000	11,688,000	2,810,000	25,845,000
Estimated Unrealized Loss, Less than 12 months	204,000	57,000	204,000	57,000	558,000
Fair Value, 12 months or greater	725,000	4,645,000	725,000	4,645,000	700,000
Estimated Unrealized Loss, 12 months or greater	49,000	110,000	49,000	110,000	57,000
Fair Value, Total	12,413,000	7,455,000	12,413,000	7,455,000	26,545,000
Estimated Unrealized Loss, Total	253,000	167,000	253,000	167,000	615,000
Fair value of total securities available-for-sale	357,804,000	360,422,000	357,804,000	360,422,000	343,380,000
Number of securities in the unrealized loss position	12	9	12	9	36
Other debt securities
Available-for-sale securities
Fair Value, Less than 12 months		4,585,000		4,585,000
Estimated Unrealized Loss, Less than 12 months		31,000		31,000
Fair Value, 12 months or greater	15,756,000	16,933,000	15,756,000	16,933,000	14,407,000
Estimated Unrealized Loss, 12 months or greater	7,451,000	6,593,000	7,451,000	6,593,000	8,952,000
Fair Value, Total	15,756,000	21,518,000	15,756,000	21,518,000	14,407,000
Estimated Unrealized Loss, Total	7,451,000	6,624,000	7,451,000	6,624,000	8,952,000
Fair value of total securities available-for-sale	44,121,000	67,147,000	44,121,000	67,147,000	43,630,000
Number of securities in the unrealized loss position	1	2	1	2	1
Collateralized debt obligations
Available-for-sale securities
Estimated Unrealized Loss, Total	7,300,000		7,300,000
Total debt securities
Available-for-sale securities
Fair value of total securities available-for-sale	$ 6,341,943,000	$ 4,749,588,000	$ 6,341,943,000	$ 4,749,588,000	$ 5,710,239,000
Number of securities in the unrealized loss position	62	50	62	50	109