Stockholders' Investment (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015
Stockholders' investment:
Beginning balance		$ 557,471	$ 537,053	$ 556,439		$ 524,287
Net Income	[1]	(2,739)	10,571	(1,839)	[2]	20,391	[2]
Share-based compensation		577	825	1,126		1,621
Issuance of restricted stock units, net of taxes paid		(13)	(22)	(177)		(861)
Issuance of common stock from stock options		0	1,833	0		4,011
(Tax deficiency) excess tax benefit on share-based compensation		(32)	380	(285)		1,191
Ending balance		$ 555,264	$ 550,640	$ 555,264		$ 550,640

[1] See Note 13 “Restatement of Previously Issued Financial Statements

[2] See Note 13 “Restatement of Previously Issued Financial Statements.”