Consolidated Statements of Changes in Shareholders’ Equity and Comprehensive Income (USD $) In Thousands, unless otherwise specified	Common Stock [Member]	Preferred Stock [Member]	Accumulated Deferred Compensation [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2008	$ 352,265		$ 2,409	$ 1,040	$ 54,138	$ 409,852
Balance (in Shares) at Dec. 31, 2008	28,880
Issuance of preferred stock and related warrants	1,207	82,519				83,726
Redemption of preferred stock		(83,726)				(83,726)
Preferred stock dividends and discount accretion		1,207			(3,963)	(2,756)
Exercise of stock options	9,610					9,610
Exercise of stock options (in Shares)	361
Tax benefits increase (decrease) upon exercise of stock option	2,188					2,188
Restricted stock activity	251		76			327
Restricted stock activity (in Shares)	7
Stock based compensation	1,132					1,132
Stock awarded to employees	102					102
Stock awarded to employees (in Shares)	2
Purchase and retirement of stock	(508)				(1,538)	(2,046)
Purchase and retirement of stock (in Shares)	(42)
Dividends					(41,061)	(41,061)
Comprehensive income
Net income for the year					125,426	125,426
Other comprehensive income,
Increase (decrease) in net unrealized gain on securities available for sale				2,638		2,638
Post-retirement benefit transition obligation amortization				36		36
Total comprehensive income						128,100
Balance at Dec. 31, 2009	366,247		2,485	3,714	133,002	505,448
Balance (in Shares) at Dec. 31, 2009	29,208
Exercise of stock options	16,688					16,688
Exercise of stock options (in Shares)	406
Tax benefits increase (decrease) upon exercise of stock option	1,004					1,004
Restricted stock activity	194		239			433
Restricted stock activity (in Shares)	7
Stock based compensation	1,380					1,380
Stock awarded to employees	125					125
Stock awarded to employees (in Shares)	2
Purchase and retirement of stock	(6,753)				(21,966)	(28,719)
Purchase and retirement of stock (in Shares)	(533)
Dividends					(42,094)	(42,094)
Comprehensive income
Net income for the year					94,577	94,577
Other comprehensive income,
Increase (decrease) in net unrealized gain on securities available for sale				(3,591)		(3,591)
Post-retirement benefit transition obligation amortization				36		36
Total comprehensive income						91,022
Balance at Dec. 31, 2010	378,885		2,724	159	163,519	545,287
Balance (in Shares) at Dec. 31, 2010	29,090
Exercise of stock options	14,374					14,374
Exercise of stock options (in Shares)	360					360
Tax benefits increase (decrease) upon exercise of stock option	(248)					(248)
Restricted stock activity	455		336			791
Restricted stock activity (in Shares)	15
Stock based compensation	1,425					1,425
Stock awarded to employees	89					89
Stock awarded to employees (in Shares)	2
Purchase and retirement of stock	(17,205)				(43,300)	(60,505)
Purchase and retirement of stock (in Shares)	(1,317)
Dividends					(41,670)	(41,670)
Comprehensive income
Net income for the year					87,888	87,888
Other comprehensive income,
Increase (decrease) in net unrealized gain on securities available for sale				11,174		11,174
Post-retirement benefit transition obligation amortization				36		36
Total comprehensive income						99,098
Balance at Dec. 31, 2011	$ 377,775		$ 3,060	$ 11,369	$ 166,437	$ 558,641
Balance (in Shares) at Dec. 31, 2011	28,150