Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other comprehensive loss	Treasury Stock	Total
Balance at Dec. 31, 2016	$ 1,395	$ 2,484,251	$ 78,850	$ (88,011)		$ 2,476,485
Balance (in shares) at Dec. 31, 2016	139,530,654
Increase (Decrease) in Stockholders' Equity
Net income			171,998			171,998
Cash dividends declared ($0.72 and $0.66 per share for nine months ended September 30, 2018 and 2017, respectively)			(92,101)			(92,101)
Common stock issued under Employee Stock Purchase Plan		528				528
Common stock issued under Employee Stock Purchase Plan (in shares)	15,961
Equity-based awards	$ 1	4,494	(444)			4,051
Equity-based awards (in shares)	39,667
Other comprehensive (loss) income, net of tax				20,897		20,897
Balance at Sep. 30, 2017	$ 1,396	2,489,273	158,303	(67,114)		2,581,858
Balance (in shares) at Sep. 30, 2017	139,586,282
Balance at Jun. 30, 2017				(67,651)
Increase (Decrease) in Stockholders' Equity
Net income						58,363
Other comprehensive (loss) income, net of tax				537		537
Balance at Sep. 30, 2017	$ 1,396	2,489,273	158,303	(67,114)		2,581,858
Balance (in shares) at Sep. 30, 2017	139,586,282
Balance at Dec. 31, 2017	$ 1,396	2,488,643	139,177	(96,383)	$ (282)	$ 2,532,551
Balance (in shares) at Dec. 31, 2017	139,588,782					139,588,782
Increase (Decrease) in Stockholders' Equity
Net income			204,399			$ 204,399
Cash dividends declared ($0.72 and $0.66 per share for nine months ended September 30, 2018 and 2017, respectively)			(98,666)			(98,666)
Common stock issued under Employee Stock Purchase Plan		342				342
Common stock issued under Employee Stock Purchase Plan (in shares)	12,341
Equity-based awards	$ 1	5,451	(515)		(53)	4,884
Equity-based awards (in shares)	42,475
Common stock repurchased					(131,800)	(131,800)
Common stock repurchased (in shares)	(4,769,870)
Other comprehensive (loss) income, net of tax				(88,248)		(88,248)
Balance at Sep. 30, 2018	$ 1,397	2,494,436	264,463	(204,699)	(132,135)	$ 2,423,462
Balance (in shares) at Sep. 30, 2018	134,873,728					134,873,728
Balance at Jun. 30, 2018				(182,410)
Increase (Decrease) in Stockholders' Equity
Net income						$ 67,388
Other comprehensive (loss) income, net of tax				(22,289)		(22,289)
Balance at Sep. 30, 2018	$ 1,397	$ 2,494,436	264,463	(204,699)	$ (132,135)	$ 2,423,462
Balance (in shares) at Sep. 30, 2018	134,873,728					134,873,728
Increase (Decrease) in Stockholders' Equity
Adoption of Accounting Standards Update No. 2018-02			$ 20,068	$ (20,068)