Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010 Hedges		Dec. 31, 2009 Hedges
Net unrealized gains/losses on cash flow hedges, before tax amount:
Net unrealized gains/losses arising during the year on cash flow hedges, before tax amount	$ (11,316,000)		$ (20,459,000)		$ (31,887,000)
Valuation allowance for the change in deferred taxes arising from unrealized gains/losses on cash flow hedges, before tax amount	0	[1]	0	[1]	0	[1]
Net unrealized gains/losses on cash flow hedges, before tax amount	(11,316,000)		(20,459,000)		(31,887,000)
Net unrealized gains/losses on investment securities available for sale, before tax amount:
Unrealized gains/losses arising during the year on investment securities available for sale, before tax amount	50,258,000		(9,991,000)		(25,292,000)
Reclassification adjustment for (gains)/losses realized in net income on investment securities available for sale, before tax amount	(75,007,000)		1,271,000		(14,067,000)
Valuation allowance for the change in deferred taxes arising from unrealized gains/losses on investment securities available for sale, before tax amount	0	[1]	0	[1]	0	[1]
Net unrealized gains/losses on investment securities available for sale, before tax amount	(24,749,000)		(8,720,000)		(39,359,000)
Amortization of post-retirement unfunded health benefit, before tax amount	0		2,470,000		35,000
Other comprehensive income (loss), before tax amount	(36,065,000)		(26,709,000)		(71,211,000)
Net unrealized gains/losses on cash flow hedges, tax (expense) benefit:
Net unrealized gains/losses arising during the year on cash flow hedges, tax (expense) benefit	4,279,000		7,867,000		12,404,000
Valuation allowance for the change in deferred taxes arising from unrealized gains/losses on cash flow hedges, tax (expense) benefit	(4,279,000)	[1]	(7,858,000)	[1]	0	[1]
Net unrealized gains/losses on cash flow hedges, tax (expense) benefit	0		9,000		12,404,000
Net unrealized gains/losses on investment securities available for sale, tax (expense) benefit:
Unrealized gains/losses arising during the year on investment securities available for sale, tax (expense) benefit	(19,349,000)		3,889,000		8,991,000
Reclassification adjustment for (gains)/losses realized in net income on investment securities available for sale, tax (expense) benefit	29,271,000		(494,000)		5,383,000
Valuation allowance for the change in deferred taxes arising from unrealized gains/losses on investment securities available for sale, tax (expense) benefit	(9,922,000)	[1]	(3,393,000)	[1]	0	[1]
Net unrealized gains/losses on investment securities available for sale, tax (expense) benefit	0		2,000		14,374,000
Amortization of post-retirement unfunded health benefit, tax (expense) benefit	0		(950,000)		(14,000)
Other comprehensive income (loss), tax(expense) benefit	0		(939,000)		26,764,000
Net unrealized gains/losses on cash flow hedges, net of tax amount:
Net unrealized gains/losses arising during the year on cash flow hedges, net of tax amount	(7,037,000)		(12,592,000)		(19,483,000)
Valuation allowance for the change in deferred taxes arising from unrealized gains/losses on cash flow hedges, net of tax amount	(4,279,000)	[1]	(7,858,000)	[1]	0	[1]
Net unrealized gains/losses on cash flow hedges, net of tax amount	(11,316,000)		(20,450,000)		(19,483,000)
Net unrealized gains/losses on investment securities available for sale, net of tax amount:
Unrealized gains/losses arising during the year on investment securities available for sale, net of tax amount	30,909,000		(6,102,000)		(16,301,000)
Reclassification adjustment for (gains)/losses realized in net income on investment securities available for sale, net of tax amount	(45,736,000)		777,000		(8,684,000)
Valuation allowance for the change in deferred taxes arising from unrealized gains/losses on investment securities available for sale, net of tax amount	(9,922,000)	[1]	(3,393,000)	[1]	0	[1]
Net unrealized gains/losses on investment securities available for sale, net of tax amount	(24,749,000)		(8,718,000)		(24,985,000)
Amortization of post-retirement unfunded health benefit, net of tax amount	0		1,520,000		21,000
Other comprehensive (loss) income	(36,065,000)		(27,648,000)		(44,447,000)
Cash settlements on cash flow hedges	3,200,000		15,800,000		33,400,000
Cash receipts on terminated cash flow hedges			14,600,000		10,300,000
Number of cash flow hedges terminated			4		3
Amortization on previously terminated cash flow hedge settlemants, before tax	9,200,000		10,000,000		4,000,000
Change in unrealized gain (loss) on cash flow hedges, before tax	$ (2,300,000)		$ (10,300,000)		$ (27,800,000)

[1] In accordance with ASC 740-20-45-11(b), the deferred tax asset valuation allowance associated with unrealized gains and losses not recognized in income is charged directly to other comprehensive income /(loss).