Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other comprehensive Income (loss)	Treasury Stock	Total
Increase (Decrease) in Stockholders' Equity
Adoption of Accounting Standards Update No. 2018-02			$ 20,068	$ (20,068)
Balance, beginning 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
Increase (Decrease) in Stockholders' Equity
Net income			204,399			204,399
Cash dividends declared			(98,666)			(98,666)
Equity-based awards	$ 1	5,451	(515)		(53)	4,884
Equity-based awards (in shares)	42,475
Other comprehensive income (loss), net of tax				(88,248)		(88,248)
Common stock issued under Employee Stock Purchase Plan		342				342
Common stock issued under Employee Stock Purchase Plan (in shares)	12,341
Common stock repurchased					(131,800)	(131,800)
Common stock repurchased (in shares)	(4,769,870)
Balance, ending 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
Balance, beginning at Jun. 30, 2018	$ 1,396	2,492,656	229,615	(182,410)	(82,082)	2,459,175
Balance (in shares) at Jun. 30, 2018	136,642,060
Increase (Decrease) in Stockholders' Equity
Net income			67,388			67,388
Cash dividends declared			(32,370)			(32,370)
Equity-based awards	$ 1	1,780	(170)		(53)	1,558
Equity-based awards (in shares)	33,469
Other comprehensive income (loss), net of tax				(22,289)		(22,289)
Common stock repurchased					(50,000)	(50,000)
Common stock repurchased (in shares)	(1,801,801)
Balance, ending 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
Balance, beginning at Dec. 31, 2018	$ 1,397	2,495,853	291,919	(132,195)	(132,135)	$ 2,524,839
Balance (in shares) at Dec. 31, 2018	134,874,302					134,874,302
Increase (Decrease) in Stockholders' Equity
Net income			216,556			$ 216,556
Cash dividends declared			(104,392)			(104,392)
Equity-based awards	$ 2	5,471	(766)		(1,764)	2,943
Equity-based awards (in shares)	185,736
Other comprehensive income (loss), net of tax				113,421		113,421
Common stock repurchased					(98,809)	(98,809)
Common stock repurchased (in shares)	(3,799,138)
Balance, ending at Sep. 30, 2019	$ 1,399	2,501,324	403,317	(18,774)	(232,708)	$ 2,654,558
Balance (in shares) at Sep. 30, 2019	131,260,900					131,260,900
Balance, beginning at Jun. 30, 2019	$ 1,399	2,499,946	363,748	(31,984)	(173,668)	$ 2,659,441
Balance (in shares) at Jun. 30, 2019	133,508,212
Increase (Decrease) in Stockholders' Equity
Net income			74,199			74,199
Cash dividends declared			(34,408)			(34,408)
Equity-based awards		1,378	(222)		(231)	925
Equity-based awards (in shares)	41,980
Other comprehensive income (loss), net of tax				13,210		13,210
Common stock repurchased					(58,809)	(58,809)
Common stock repurchased (in shares)	(2,289,292)
Balance, ending at Sep. 30, 2019	$ 1,399	$ 2,501,324	$ 403,317	$ (18,774)	$ (232,708)	$ 2,654,558
Balance (in shares) at Sep. 30, 2019	131,260,900					131,260,900