Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2011	Oct. 31, 2011	Dec. 31, 2011	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Jan. 24, 2008
Shareholders' Equity
Number of shares authorized to be repurchased										1,000,000
Number of shares that may yet be purchased	1,140,400		1,140,400	1,140,400
Components of AOCI
Net unrealized gain on securities available-for-sale	$ 73,235		$ 73,235	$ 73,235		$ 36,386
Net unrealized gain on cash flow hedges	222		222	222		1,184
Pension liability adjustment	(1,085)		(1,085)	(1,085)		(717)
Total accumulated other comprehensive income	72,372		72,372	72,372		36,853
Components of total comprehensive income
Net income				174,099	[1]	133,318	[1]	53,506	[1]
Securities available-for-sale:
Net unrealized gain, net of taxes of $28,254, $34,592, and $41,336, and reclassification of $2,882, ($5,170), and ($668) included in net income				39,291		48,104		57,482
Net unrealized gain (loss) on securities available-for-sale, tax expense (benefit)				28,254		34,592		41,336
Net unrealized gain (loss) on securities available-for-sale, reclassification of net gain (loss) included in net income				2,882		(5,170)		(668)
Non-credit related impairment loss, net of taxes of ($1,756), ($3,130), and ($7,181)				(2,442)		(4,352)		9,987
Non-credit related impairment loss on investment securities, tax benefit				(1,756)		(3,130)		(7,181)
Net unrealized loss on cash flow hedges, net of taxes of $0, $3,134, and $1,706, and reclassification of $559, $4,956, and $6,996 included in net income				(962)		(3,187)		(2,658)
Net unrealized gain (loss) on cash flow hedges, tax expense (benefit)				0		3,134		1,706
Net unrealized gain (loss) on cash flow hedges, reclassification of net gain included in net income				559		4,956		6,996
Pension liability adjustment				(368)		(663)		136
Total other comprehensive income				35,519	[2]	39,902	[2]	44,973	[2]
Total comprehensive income				209,618		173,220		98,479
Net income (loss) attributable to redeemable noncontrolling interest				$ 1,956		$ 1,779		$ (1,457)
Common shares repurchased
Total number of Shares (or Units) Purchased (in shares)	806	537	1,343
Average Price Paid per Share (or Unit) (in dollars per share)	$ 41.90	$ 40.54	$ 41.36
Shares of common stock reserved for issuance under share-based compensation arrangements (in shares)	1,400,000		1,400,000	1,400,000
Shares of unvested restricted stock (in shares)	700,000		700,000	700,000

[1] Net income excludes net income (loss) attributable to redeemable noncontrolling interest of $1,956, $1,779 and ($1,457) during 2011, 2010 and 2009, respectively. Redeemable noncontrolling interest is reflected in the mezzanine section in the consolidated balance sheets. See Note 21 of the Notes to Consolidated Financial Statements.

[2] See Note 12 for additional information on other comprehensive income.