Consolidated Statements of Changes in Shareholders' Equity (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, 2010	$ 1,642,574	$ 1,540,928	$ 76,701	$ 24,945
BALANCE, SHARES at Dec. 31, 2010		114,536,814
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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 tax benefit, shares		185,133
Issuances of common stock under stock plans and related tax benefit, value	(46)	(46)
Cash dividends on common stock	(27,471)		(27,471)
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	98,361		98,361
Other comprehensive income, net of tax	(29,322)			(29,322)
Comprehensive income	69,039
Stock-based compensation	5,017	5,017
Stock repurchased and retired, shares		(584,677)
Stock repurchased and retired, value	(9,360)	(9,360)
Issuances of common stock under stock plans and related tax benefit, shares		667,921
Issuances of common stock under stock plans and related tax benefit, value	6,428	6,428
Cash dividends on common stock	(67,737)		(67,737)
BALANCE, VALUE at Dec. 31, 2013	$ 1,727,426	$ 1,514,485	$ 217,917	$ (4,976)
BALANCE, SHARES at Dec. 31, 2013	111,973,203	111,973,203