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, 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	23,232			23,232
Other comprehensive income	7,746				7,746
Dividends declared on common stock	(10,115)			(10,115)
Stock compensation expense	3,279		3,279
Net issuance of treasury stock for vested restricted stock units (in shares)		91
Net issuance of treasury stock for vested restricted stock units	(3,231)		(914)			(2,317)
Ending Balance at Mar. 31, 2017	490,326	$ 876	252,128	1,571,711	(216,110)	(1,118,279)
Ending Balance (in shares) at Mar. 31, 2017		55,142
Beginning Balance at Dec. 31, 2017	766,065	$ 1,751	262,201	1,809,845	(188,973)	(1,118,759)
Beginning Balance (in shares) at Dec. 31, 2017		110,385
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standards update for revenue recognition	9,061			9,061
Net income	45,721			45,721
Other comprehensive income	14,266				14,266
Dividends declared on common stock	(11,276)			(11,276)
Stock compensation expense	3,700		3,700
Net issuance of treasury stock for vested restricted stock units (in shares)		184
Net issuance of treasury stock for vested restricted stock units	(2,746)		(879)			(1,867)
Ending Balance at Mar. 31, 2018	$ 824,791	$ 1,751	$ 265,022	$ 1,853,351	$ (174,707)	$ (1,120,626)
Ending Balance (in shares) at Mar. 31, 2018		110,569