Summary of Operations and Significant Accounting Policies - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings (numerator)
Net (loss) income attributable to common stockholders	$ (30,651)	$ 14,450	$ 13,179	$ 1,217	$ 1,268	$ 10,648	$ 5,752	$ (1,733)	$ (1,805)	$ 15,935	$ 24,274
Shares (denominator)
Weighted average common shares outstanding (basic)									48,824	48,597	48,210
Dilutive effect of stock options and stock awards outstanding										1,192	1,290
Adjusted weighted average common shares outstanding (diluted)									48,824	49,789	49,500
(Loss) earnings per share attributable to common stockholders
Basic	$ (0.62)	$ 0.29	$ 0.27	$ 0.03	$ 0.07	$ 0.22	$ 0.12	$ (0.04)	$ (0.04)	$ 0.33	$ 0.50
Diluted	$ (0.62)	$ 0.29	$ 0.26	$ 0.02	$ 0.07	$ 0.21	$ 0.12	$ (0.04)	$ (0.04)	$ 0.32	$ 0.49