Condensed Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning Balance at Dec. 31, 2015	$ 639,184	$ 876	$ 237,291	$ 1,446,193	$ (208,806)	$ (836,370)
Beginning Balance (in shares) at Dec. 31, 2015		60,393
Increase (Decrease) in Stockholders' Equity
Net income	129,655			129,655
Other comprehensive income	13,544				13,544
Dividends declared on common stock	(31,344)			(31,344)
Stock compensation expense	9,724		9,724
Adoption of accounting standard update related to stock compensation accounting	525		598	(73)
Net issuance of treasury stock for vested restricted stock units	$ (2,434)		(892)			(1,542)
Treasury Stock, Shares, Acquired	(147)
Net issuance of treasury stock for vested restricted stock units (in shares)		94
Repurchases of common stock	$ (7,200)					(7,200)
Ending Balance at Sep. 30, 2016	751,654	$ 876	246,721	1,544,431	(195,262)	(845,112)
Ending Balance (in shares) at Sep. 30, 2016		60,340
Beginning Balance at Dec. 31, 2016	469,415	$ 876	249,763	1,558,594	(223,856)	(1,115,962)
Beginning Balance (in shares) at Dec. 31, 2016		55,051
Increase (Decrease) in Stockholders' Equity
Net income	123,539			123,539
Other comprehensive income	53,593				53,593
Dividends declared on common stock	(30,373)			(30,373)
Stock compensation expense	11,052		11,052
Net issuance of treasury stock for vested restricted stock units	(4,123)		(1,287)			(2,836)
Net issuance of treasury stock for vested restricted stock units (in shares)		180
Two-for-one stock split		$ 875	(875)
Two-for-one stock split (in shares)		55,142
Ending Balance at Sep. 30, 2017	$ 623,103	$ 1,751	$ 258,653	$ 1,651,760	$ (170,263)	$ (1,118,798)
Ending Balance (in shares) at Sep. 30, 2017		110,373