Condensed Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Total
BALANCE, VALUE at Dec. 31, 2010	$ 1,540,928	$ 76,701	$ 24,945	$ 1,642,574
BALANCE, SHARES at Dec. 31, 2010	114,536,814
Net income		74,496		74,496
Other comprehensive income, net of tax			8,829	8,829
Comprehensive income				83,325
Stock-based compensation	3,785			3,785
Stock repurchased and retired, shares	(2,557,056)
Stock repurchased and retired, value	(29,754)			(29,754)
Issuances of common stock under stock plans and related net tax deficiencies, shares	185,133
Issuances of common stock under stock plans and related net tax deficiencies, value	(46)			(46)
Cash dividends on common stock		(27,471)		(27,471)
BALANCE, VALUE at Dec. 31, 2011	1,514,913	123,726	33,774	1,672,413
BALANCE, SHARES at Dec. 31, 2011	112,164,891			112,164,891
Net income		25,503		25,503
Other comprehensive income, net of tax			1,165	1,165
Comprehensive income				26,668
Stock-based compensation	916			916
Stock repurchased and retired, shares	(395,904)
Stock repurchased and retired, value	(5,013)			(5,013)
Issuances of common stock under stock plans and related net tax deficiencies, shares	123,982
Issuances of common stock under stock plans and related net tax deficiencies, value	(42)			(42)
Cash dividends on common stock		(7,890)		(7,890)
BALANCE, VALUE at Mar. 31, 2012	$ 1,510,774	$ 141,339	$ 34,939	$ 1,687,052
BALANCE, SHARES at Mar. 31, 2012	111,892,969			111,892,969