Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Allowance for loan losses [Roll Forward]
Beginning balance	$ 190,690,000	$ 203,124,000	$ 185,396,000	$ 215,507,000
Provision for loan losses	78,000	(8,500,000)	858,000	(16,189,000)
Loans charged off	(2,638,000)	(4,708,000)	(9,008,000)	(22,169,000)
Recoveries	3,114,000	4,409,000	13,998,000	17,176,000
Ending balance	191,244,000	194,325,000	191,244,000	194,325,000
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	1,308,000	1,604,000	2,088,000	1,915,000
Provision for off-balance sheet credit losses	(78,000)	0	(858,000)	(311,000)
Ending balance	1,230,000	1,604,000	1,230,000	1,604,000
Total provision for credit losses	0	(8,500,000)	0	(16,500,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	13,587,188,000	12,237,773,000	13,587,188,000	12,237,773,000	12,691,892,000
Individually measured for impairment, recorded investment	96,551,000	112,327,000	96,551,000	112,327,000	100,372,000
Total	13,683,739,000	12,350,100,000	13,683,739,000	12,350,100,000	12,792,264,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	159,952,000	152,169,000	159,952,000	152,169,000	156,229,000
Individually measured for impairment, related allowance	3,348,000	1,274,000	3,348,000	1,274,000	954,000
Total measured for impairment, related allowance	191,244,000	194,325,000	191,244,000	194,325,000
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	87,806,000	64,044,000	79,180,000	65,280,000
Provision for loan losses	(1,174,000)	(1,774,000)	4,444,000	(3,507,000)
Loans charged off	(117,000)	(1,354,000)	(290,000)	(6,190,000)
Recoveries	260,000	864,000	3,441,000	6,197,000
Ending balance	86,775,000	61,780,000	86,775,000	61,780,000
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	345,000	402,000	119,000	475,000
Provision for off-balance sheet credit losses	(65,000)	(228,000)	161,000	(301,000)
Ending balance	280,000	174,000	280,000	174,000
Total provision for credit losses	(1,239,000)	(2,002,000)	4,605,000	(3,808,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	8,555,634,000	7,551,553,000	8,555,634,000	7,551,553,000	7,926,461,000
Individually measured for impairment, recorded investment	16,404,000	19,522,000	16,404,000	19,522,000	16,760,000
Total	8,572,038,000	7,571,075,000	8,572,038,000	7,571,075,000	7,943,221,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	83,609,000	61,208,000	83,609,000	61,208,000	78,607,000
Individually measured for impairment, related allowance	3,166,000	572,000	3,166,000	572,000	573,000
Total measured for impairment, related allowance	86,775,000	61,780,000	86,775,000	61,780,000
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	41,252,000	49,687,000	41,573,000	54,884,000
Provision for loan losses	(84,000)	(6,279,000)	(4,633,000)	(10,077,000)
Loans charged off	(145,000)	(419,000)	(365,000)	(5,669,000)
Recoveries	1,410,000	2,073,000	5,858,000	5,924,000
Ending balance	42,433,000	45,062,000	42,433,000	45,062,000
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	902,000	1,178,000	1,876,000	1,353,000
Provision for off-balance sheet credit losses	10,000	202,000	(964,000)	27,000
Ending balance	912,000	1,380,000	912,000	1,380,000
Total provision for credit losses	(74,000)	(6,077,000)	(5,597,000)	(10,050,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	2,693,539,000	2,296,727,000	2,693,539,000	2,296,727,000	2,374,503,000
Individually measured for impairment, recorded investment	30,660,000	52,502,000	30,660,000	52,502,000	40,850,000
Total	2,724,199,000	2,349,229,000	2,724,199,000	2,349,229,000	2,415,353,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	42,358,000	44,574,000	42,358,000	44,574,000	41,440,000
Individually measured for impairment, related allowance	75,000	488,000	75,000	488,000	133,000
Total measured for impairment, related allowance	42,433,000	45,062,000	42,433,000	45,062,000
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	27,654,000	39,206,000	29,465,000	41,703,000
Provision for loan losses	185,000	(136,000)	136,000	187,000
Loans charged off	(773,000)	(961,000)	(3,611,000)	(4,797,000)
Recoveries	150,000	188,000	1,226,000	1,204,000
Ending balance	27,216,000	38,297,000	27,216,000	38,297,000
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	43,000	6,000	90,000	78,000
Provision for off-balance sheet credit losses	(19,000)	42,000	(66,000)	(30,000)
Ending balance	24,000	48,000	24,000	48,000
Total provision for credit losses	166,000	(94,000)	70,000	157,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	1,930,756,000	1,996,086,000	1,930,756,000	1,996,086,000	2,010,483,000
Individually measured for impairment, recorded investment	48,907,000	38,679,000	48,907,000	38,679,000	41,543,000
Total	1,979,663,000	2,034,765,000	1,979,663,000	2,034,765,000	2,052,026,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	27,109,000	38,083,000	27,109,000	38,083,000	29,217,000
Individually measured for impairment, related allowance	107,000	214,000	107,000	214,000	248,000
Total measured for impairment, related allowance	27,216,000	38,297,000	27,216,000	38,297,000
Consumer [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	7,029,000	7,738,000	6,965,000	9,453,000
Provision for loan losses	156,000	1,256,000	1,180,000	513,000
Loans charged off	(1,603,000)	(1,974,000)	(4,742,000)	(5,513,000)
Recoveries	1,294,000	1,284,000	3,473,000	3,851,000
Ending balance	6,876,000	8,304,000	6,876,000	8,304,000
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	18,000	18,000	3,000	9,000
Provision for off-balance sheet credit losses	(4,000)	(16,000)	11,000	(7,000)
Ending balance	14,000	2,000	14,000	2,000
Total provision for credit losses	152,000	1,240,000	1,191,000	506,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	407,259,000	393,407,000	407,259,000	393,407,000	380,445,000
Individually measured for impairment, recorded investment	580,000	1,624,000	580,000	1,624,000	1,219,000
Total	407,839,000	395,031,000	407,839,000	395,031,000	381,664,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	6,876,000	8,304,000	6,876,000	8,304,000	6,965,000
Individually measured for impairment, related allowance	0	0	0	0	0
Total measured for impairment, related allowance	6,876,000	8,304,000	6,876,000	8,304,000
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance					157,183,000
Ending balance	163,300,000	153,443,000	163,300,000	153,443,000	157,183,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	13,587,188,000	12,237,773,000	13,587,188,000	12,237,773,000	12,691,892,000
Individually measured for impairment, recorded investment	96,551,000	112,327,000	96,551,000	112,327,000	100,372,000
Total	13,683,739,000	12,350,100,000	13,683,739,000	12,350,100,000	12,792,264,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	159,952,000	152,169,000	159,952,000	152,169,000	156,229,000
Individually measured for impairment, related allowance	3,348,000	1,274,000	3,348,000	1,274,000	954,000
Total measured for impairment, related allowance	163,300,000	153,443,000	163,300,000	153,443,000	157,183,000
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	26,949,000	42,449,000	28,213,000	44,187,000
Provision for loan losses	995,000	(1,567,000)	(269,000)	(3,305,000)
Loans charged off	0	0	0	0
Recoveries	0	0	0	0
Ending balance	27,944,000	40,882,000	27,944,000	40,882,000
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	0	0	0	0
Provision for off-balance sheet credit losses	0	0	0	0
Ending balance	0	0	0	0
Total provision for credit losses	995,000	(1,567,000)	(269,000)	(3,305,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	0	0	0	0	0
Individually measured for impairment, recorded investment	0	0	0	0	0
Total	0	0	0	0	0
Related allowance [Abstract]
Collectively measured for impairment, related allowance	0	0	0	0	0
Individually measured for impairment, related allowance	0	0	0	0	0
Total measured for impairment, related allowance	$ 27,944,000	$ 40,882,000	$ 27,944,000	$ 40,882,000