Condensed Consolidated Statements of Changes In Shareholders' Equity (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
BALANCE, VALUE at Dec. 31, 2011	$ 1,672,413	$ 1,514,913	$ 123,726	$ 33,774
BALANCE, SHARES at Dec. 31, 2011		112,164,891
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	101,891		101,891
Other comprehensive income, net of tax	(9,428)			(9,428)
Comprehensive income	92,463
Stock-based compensation	4,041	4,041
Stock repurchased and retired, shares		(596,000)
Stock repurchased and retired, value	(7,436)	(7,436)
Issuances of common stock under stock plans and related tax benefit, shares		321,068
Issuances of common stock under stock plans and related tax benefit, value	882	882
Cash dividends on common stock	(38,324)		(38,324)
BALANCE, VALUE at Dec. 31, 2012	1,724,039	1,512,400	187,293	24,346
BALANCE, SHARES at Dec. 31, 2012	111,889,959	111,889,959
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	73,091		73,091
Other comprehensive income, net of tax	(21,173)			(21,173)
Comprehensive income	51,918
Stock-based compensation	3,531	3,531
Stock repurchased and retired, shares		(319,164)
Stock repurchased and retired, value	(4,704)	(4,704)
Issuances of common stock under stock plans and related tax benefit, shares		357,967
Issuances of common stock under stock plans and related tax benefit, value	1,998	1,998
Cash dividends on common stock	(50,787)		(50,787)
BALANCE, VALUE at Sep. 30, 2013	$ 1,725,995	$ 1,513,225	$ 209,597	$ 3,173
BALANCE, SHARES at Sep. 30, 2013	111,928,762	111,928,762