Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Share Repurchase Program [Member]	Accelerated Stock Repurchase Program [Member]	Common Stock [Member]	Common Stock [Member] Share Repurchase Program [Member]	Common Stock [Member] Accelerated Stock Repurchase Program [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Accelerated Stock Repurchase Program [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Treasury Stock [Member] Share Repurchase Program [Member]	Treasury Stock [Member] Accelerated Stock Repurchase Program [Member]
Beginning Balance at Dec. 31, 2014	$ 1,996,665			$ 545,555			$ 1,420,523		$ 558,810	$ (17,722)	$ (510,501)
Beginning Balance (in shares) at Dec. 31, 2014				178,924
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	110,967								110,967
Other comprehensive income	4,503									4,503
Stock issued, including related tax benefits	6,938			$ 889			2,675				3,374
Stock issued, including related tax benefits (in shares)				613
Stock-based compensation awards	4,371						4,371
Acquisition of treasury stock (in shares)				(3,976)		(1,790)
Acquisition of treasury stock	(50,000)		$ 0					$ 20,000			(50,000)		$ (20,000)
Common stock cash dividends	(47,540)								(47,540)
Ending Balance at Sep. 30, 2015	2,025,904			$ 546,444			1,447,569		622,237	(13,219)	(577,127)
Ending Balance (in shares) at Sep. 30, 2015				173,771
Beginning Balance at Dec. 31, 2015	2,041,894			$ 547,141			1,450,690		641,588	(22,017)	(575,508)
Beginning Balance (in shares) at Dec. 31, 2015				174,176
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	119,475								119,475
Other comprehensive income	26,508									26,508
Stock issued, including related tax benefits	5,526			$ 594			2,099				2,833
Stock issued, including related tax benefits (in shares)				454
Stock-based compensation awards	4,808						4,808
Acquisition of treasury stock (in shares)					(1,486)
Acquisition of treasury stock		$ (18,545)										$ (18,545)
Common stock cash dividends	(50,230)								(50,230)
Ending Balance at Sep. 30, 2016	$ 2,129,436			$ 547,735			$ 1,457,597		$ 710,833	$ 4,491	$ (591,220)
Ending Balance (in shares) at Sep. 30, 2016				173,144