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			113,635			113,635
Cash dividends declared ($0.48 and $0.44 per share for six months ended June 30, 2018 and 2017, respectively)			(61,400)			(61,400)
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		3,312	(318)			2,994
Other comprehensive (loss) income, net of tax				20,360		20,360
Balance at Jun. 30, 2017	$ 1,395	2,488,091	130,767	(67,651)		2,552,602
Balance (in shares) at Jun. 30, 2017	139,546,615
Balance at Mar. 31, 2017				(86,692)
Increase (Decrease) in Stockholders' Equity
Net income						56,895
Other comprehensive (loss) income, net of tax				19,041		19,041
Balance at Jun. 30, 2017	$ 1,395	2,488,091	130,767	(67,651)		2,552,602
Balance (in shares) at Jun. 30, 2017	139,546,615
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			137,011			$ 137,011
Cash dividends declared ($0.48 and $0.44 per share for six months ended June 30, 2018 and 2017, respectively)			(66,296)			(66,296)
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		3,671	(345)			3,326
Equity-based awards (in shares)	9,006
Common stock repurchased					(81,800)	(81,800)
Common stock repurchased (in shares)	(2,968,069)
Other comprehensive (loss) income, net of tax				(65,959)		(65,959)
Balance 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					136,642,060
Balance at Mar. 31, 2018				(164,684)
Increase (Decrease) in Stockholders' Equity
Net income						$ 69,053
Other comprehensive (loss) income, net of tax				(17,726)		(17,726)
Balance 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					136,642,060
Increase (Decrease) in Stockholders' Equity
Adoption of ASU | ASU 2018-02			$ 20,068	$ (20,068)