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	59,886			59,886
Other comprehensive income	6,510				6,510
Dividends declared on common stock	(20,913)			(20,913)
Stock compensation expense	6,428		6,428
Adoption of accounting standard update related to stock compensation accounting	525		598	(73)
Net issuance of treasury stock for vested restricted stock units	(2,204)		(802)			(1,402)
Net issuance of treasury stock for vested restricted stock units (in shares)		84
Repurchases of common stock	(10)					(10)
Ending Balance at Jun. 30, 2016	689,406	$ 876	243,515	1,485,093	(202,296)	(837,782)
Ending Balance (in shares) at Jun. 30, 2016		60,477
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	51,157			51,157
Other comprehensive income	38,717				38,717
Dividends declared on common stock	(20,253)			(20,253)
Stock compensation expense	7,202		7,202
Net issuance of treasury stock for vested restricted stock units	(3,231)		(1,013)			(2,218)
Net issuance of treasury stock for vested restricted stock units (in shares)		123
Two-for-one stock split		$ 875	(875)
Two-for-one stock split (in shares)		55,142
Ending Balance at Jun. 30, 2017	$ 543,007	$ 1,751	$ 255,077	$ 1,589,498	$ (185,139)	$ (1,118,180)
Ending Balance (in shares) at Jun. 30, 2017		110,316