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	76,716								76,716
Other comprehensive income	(5,155)									(5,155)
Stock issued, including related tax benefits	4,695			$ 664			1,954				2,077
Stock issued, including related tax benefits (in shares)				423
Stock-based compensation awards	2,838						2,838
Acquisition of treasury stock (in shares)				(1,538)		(1,790)
Acquisition of treasury stock	(19,013)		$ 0					$ 20,000			(19,013)		$ (20,000)
Common stock cash dividends	(31,929)								(31,929)
Ending Balance at Jun. 30, 2015	2,024,817			$ 546,219			1,445,315		603,597	(22,877)	(547,437)
Ending Balance (in shares) at Jun. 30, 2015				176,019
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	78,007								78,007
Other comprehensive income	29,706									29,706
Stock issued, including related tax benefits	3,348			$ 389			1,405				1,554
Stock issued, including related tax benefits (in shares)				273
Stock-based compensation awards	3,256						3,256
Acquisition of treasury stock (in shares)					(1,310)
Acquisition of treasury stock		$ (16,254)										$ (16,254)
Common stock cash dividends	(32,960)								(32,960)
Ending Balance at Jun. 30, 2016	$ 2,106,997			$ 547,530			$ 1,455,351		$ 686,635	$ 7,689	$ (590,208)
Ending Balance (in shares) at Jun. 30, 2016				173,139