Supplementary Information - Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 115,385	$ 91,057	$ 75,498	$ 114,813	$ 127,771	$ 88,132	$ 77,029	$ 113,252
Gross profit	50,715	38,506	33,648	58,871	62,444	41,315	38,378	61,745	$ 181,740		$ 203,882	[1]	$ 211,525	[1]
Operating income (loss)	2,710	6,160	1,202	10,697	6,406	13,365	3,849	12,683	20,769		36,303	[1]	53,394	[1]
Income from continuing operations	1,460	4,503	1,007	8,140	8,532	8,342	2,566	8,185	15,110		27,625	[1],[2]	35,101	[1],[2]
Income (loss) from discontinued operation	(98)	(194)	(79)	(81)	(88)	(101)	(77)	(1,092)	(452)		(1,358)	[1],[2]	(923)	[1],[2]
Net income	$ 1,362	$ 4,309	$ 928	$ 8,059	$ 8,444	$ 8,241	$ 2,489	$ 7,093	$ 14,658		$ 26,267	[1],[2]	$ 34,178	[1],[2]
Basic (in dollars per share)	$ 0.05	$ 0.14	$ 0.03	$ 0.27	$ 0.28	$ 0.27	$ 0.08	$ 0.23	$ 0.49	[3]	$ 0.86	[1],[3]	$ 1.10	[1],[3]
Diluted (in dollars per share)	$ 0.05	$ 0.14	$ 0.03	$ 0.26	$ 0.27	$ 0.27	$ 0.08	$ 0.23	$ 0.48	[3]	$ 0.85	[1],[3]	$ 1.09	[1],[3]
Asset impairment charge									$ 0		$ 8,800	[1],[2]	$ 0	[1],[2]
Payments for legal settlements								$ 1,200	1,200
Additions for tax positions taken in prior years					$ 5,600				$ 41		$ 38		$ 21

[1] See Note 4.

[2] See Note 4.

[3] May not add due to rounding.