CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Deficit) [Member]	Accumulated Other Comprehensive Losses [Member]	Treasury Stock [Member]
BALANCES at Dec. 31, 2013	$ 322,379	$ 705	$ 625,971	$ (277,128)	$ (18)	$ (27,151)
BALANCES (in shares) at Dec. 31, 2013		68,523,419
Net income for the year	60,930	$ 0	0	60,930	0	0
Foreign currency translation	(619)	0	0	0	(619)	0
Stock-based compensation	7,718	$ 4	7,714	0	0	0
Stock-based compensation (in shares)		392,470
Stock repurchase	(1,497)	$ 0	0	0	0	(1,497)
Stock repurchase (in shares)		(113,203)
Common stock issued in connection with: Stock option exercises	1,921	$ 0	1,921	0	0	0
Common stock issued in connection with: Stock option exercises (in shares)		195,383
BALANCES at Dec. 31, 2014	390,832	$ 709	635,606	(216,198)	(637)	(28,648)
BALANCES (in shares) at Dec. 31, 2014		68,998,069
Net income for the year	104,289			104,291
Foreign currency translation	(863)				(863)
Stock-based compensation	10,010	$ 4	10,006
Stock-based compensation (in shares)		396,389
Stock repurchase	(61,757)					(61,757)
Stock repurchase (in shares)		(4,651,570)
Equity component of convertible senior notes repurchase	(4,714)		(4,714)
Common stock issued in connection with: Stock option exercises	2,012	$ 2	2,010
Common stock issued in connection with: Stock option exercises (in shares)		186,622
BALANCES at Dec. 31, 2015	439,811	$ 715	642,908	(111,907)	(1,500)	(90,405)
BALANCES (in shares) at Dec. 31, 2015		64,929,510
Net income for the year	119,433			119,433
Foreign currency translation	(1,347)				(1,347)
Stock-based compensation	12,037	$ 6	12,031
Stock-based compensation (in shares)		615,066
Stock repurchase	(79,556)					(79,556)
Stock repurchase (in shares)		(5,832,387)
Equity component of convertible senior notes repurchase	(18,883)		(18,883)
Common stock dividends	(3,935)			(3,935)
Common stock issued in connection with: Stock option exercises	4,831	$ 4	4,827
Common stock issued in connection with: Stock option exercises (in shares)		417,442
BALANCES at Dec. 31, 2016	$ 472,391	$ 725	$ 640,883	$ 3,591	$ (2,847)	$ (169,961)
BALANCES (in shares) at Dec. 31, 2016		60,129,631