Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income
Beginning Balance (in shares) at Dec. 31, 2014		88,335
Beginning Balance at Dec. 31, 2014	$ 756,043	$ 113	$ (1,016,381)	$ 877,566	$ 898,574	$ (3,829)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)	213,479				219,299	(5,820)
Purchase of treasury stock (in shares)		(12,414)
Purchase of treasury stock	(479,799)		(479,799)
Dividends declared	(59,725)				(59,725)
Exercise of stock options (in shares)		80
Exercise of stock options	1,744	$ 1		1,743
Restricted stock awards (in shares)		290
Restricted stock awards	0			0
Minimum tax withholding requirements (in shares)		(15)
Minimum tax withholding requirements	(574)			(574)
Excess tax benefit from stock-based compensation	604			604
Stock-based compensation	6,280			6,280
Exchange of convertible senior notes (Note 7)	30,509			30,509
Ending Balance (in shares) at Dec. 31, 2015		76,276
Ending Balance at Dec. 31, 2015	468,561	$ 114	(1,496,180)	916,128	1,058,148	(9,649)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)	(285,298)				(286,250)	952
Purchase of treasury stock (in shares)		(7,926)
Purchase of treasury stock	(229,169)		(229,169)
Dividends declared	(55,700)				(55,700)
Exercise of stock options (in shares)		24
Exercise of stock options	353			353
Restricted stock awards (in shares)		74
Restricted stock awards	0			0
Minimum tax withholding requirements (in shares)		(49)
Minimum tax withholding requirements	(1,169)			(1,169)
Excess tax benefit from stock-based compensation	(1,458)			(1,458)
Stock-based compensation	8,833			8,833
Ending Balance (in shares) at Dec. 31, 2016		68,399
Ending Balance at Dec. 31, 2016	(95,047)	$ 114	(1,725,349)	922,687	716,198	(8,697)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)	(145,985)				(148,851)	2,866
Restricted stock awards (in shares)		574
Restricted stock awards	1	$ 1		0
Minimum tax withholding requirements (in shares)		(32)
Minimum tax withholding requirements	(253)			(253)
Stock-based compensation	8,359			8,359
Dividend forfeitures on restricted stock	394				394
Exchange of convertible senior notes (in shares)		14,626
Exchange of convertible senior notes (Note 7)	70,537	$ 15		70,522
Ending Balance (in shares) at Dec. 31, 2017		83,567
Ending Balance at Dec. 31, 2017	$ (161,994)	$ 130	$ (1,725,349)	$ 1,001,315	$ 567,741	$ (5,831)