Condensed Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [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 loss, 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 tax deficiencies, shares	185,133
Issuances of common stock under stock plans and related 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		48,780		48,780
Other comprehensive loss, net of tax			(3,045)	(3,045)
Comprehensive income				45,735
Stock-based compensation	1,942			1,942
Stock repurchased and retired, shares	(413,750)
Stock repurchased and retired, value	(5,234)			(5,234)
Issuances of common stock under stock plans and related tax deficiencies, shares	140,142
Issuances of common stock under stock plans and related tax deficiencies, value	12			12
Cash dividends on common stock		(18,032)		(18,032)
BALANCE, VALUE at Jun. 30, 2012	$ 1,511,633	$ 154,474	$ 30,729	$ 1,696,836
BALANCE, SHARES at Jun. 30, 2012	111,891,283			111,891,283