Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other comprehensive Income (loss)	Treasury Stock	Total
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			67,958			67,958
Cash dividends declared ($0.26 and $0.24 per share for the three months ended March 31, 2019 and 2018, respectively)			(33,504)			(33,504)
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		1,925	(177)			1,748
Other comprehensive loss, net of tax				(48,233)		(48,233)
Balance, ending at Mar. 31, 2018	$ 1,396	2,490,910	193,522	(164,684)	(282)	2,520,862
Balance (in shares) at Mar. 31, 2018	139,601,123
Increase (Decrease) in Stockholders' Equity
Adoption of Accounting Standards Update No. 2018-02			20,068	(20,068)
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			69,924			$ 69,924
Cash dividends declared ($0.26 and $0.24 per share for the three months ended March 31, 2019 and 2018, respectively)			(35,067)			(35,067)
Equity-based awards	$ 2	1,917	(325)		(1,529)	65
Equity-based awards (in shares)	137,713
Other comprehensive loss, net of tax				53,441		53,441
Balance, ending at Mar. 31, 2019	$ 1,399	$ 2,497,770	$ 326,451	$ (78,754)	$ (133,664)	$ 2,613,202
Balance (in shares) at Mar. 31, 2019	135,012,015					135,012,015