Consolidated Statements Of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balances, shares at Dec. 31, 2014	52,994
Balances, value at Dec. 31, 2014	$ 1,289,625	$ 5,300	$ 649,715	$ 644,085	$ (9,475)
Stock-based compensation expense	$ 7,709		7,709
Shares repurchased and retired, shares	(3,066)
Shares repurchased and retired, value	$ (68,365)	(307)	(33,477)	(34,581)
Stock options exercised, shares	114
Stock options exercised, value	$ 1,976	11	1,965
Vesting of restricted stock units, shares	160
Vesting of restricted stock units, value		16	(16)
Shares withheld for taxes, shares	(24)
Shares withheld for taxes, value	$ (571)	(2)	(569)
Excess tax shortfall of stock-based compensation	(330)		(330)
Net income (loss)	95,401			95,401
Other comprehensive income (loss)	$ (3,541)				(3,541)
Balances, shares at Dec. 31, 2015	50,178
Balances, value at Dec. 31, 2015	$ 1,321,904	5,018	624,997	704,905	(13,016)
Stock-based compensation expense	$ 5,322		5,322
Shares repurchased and retired, shares	(1,959)
Shares repurchased and retired, value	$ (41,929)	(196)	(21,396)	(20,337)
Stock options exercised, shares	928
Stock options exercised, value	$ 18,825	93	18,732
Vesting of restricted stock units, shares	209
Vesting of restricted stock units, value		21	(21)
Shares withheld for taxes, shares	(26)
Shares withheld for taxes, value	$ (568)	(3)	(565)
Excess tax shortfall of stock-based compensation	(976)		(976)
Net income (loss)	64,047			64,047
Other comprehensive income (loss)	$ (1,160)				(1,160)
Balances, shares at Dec. 31, 2016	49,330
Balances, value at Dec. 31, 2016	$ 1,365,465	4,933	626,093	748,615	(14,176)
Cumulative effect of accounting change	0	0	213	(213)	0
Stock-based compensation expense	$ 7,815		7,815
Shares repurchased and retired, shares	(963)
Shares repurchased and retired, value	$ (29,348)	(97)	(10,676)	(18,575)
Stock options exercised, shares	582
Stock options exercised, value	$ 11,208	58	11,150
Vesting of restricted stock units, shares	206
Vesting of restricted stock units, value		21	(21)
Shares withheld for taxes, shares	(12)
Shares withheld for taxes, value	$ (383)	(1)	(382)
Net income (loss)	(31,965)			(31,965)
Other comprehensive income (loss)	$ 6,027				6,027
Balances, shares at Dec. 31, 2017	49,143
Balances, value at Dec. 31, 2017	$ 1,328,819	$ 4,914	$ 634,192	$ 697,862	$ (8,149)