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, 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
Earnings (numerator)
Net income (loss) attributable to common stockholders	$ 29,519	$ 30,908	$ 25,068	$ 18,526	$ (30,651)	$ 14,450	$ 13,179	$ 1,217	$ 104,021	$ (1,805)	$ 15,935
Shares (denominator)
Weighted average common shares outstanding (basic)									49,841	48,824	48,597
Dilutive effect of stock options and stock awards outstanding									1,094		1,192
Adjusted weighted average common shares outstanding (diluted)									50,935	48,824	49,789
Earnings (loss) per share attributable to common stockholders
Basic	$ 0.59	$ 0.62	$ 0.50	$ 0.38	$ (0.62)	$ 0.29	$ 0.27	$ 0.03	$ 2.09	$ (0.04)	$ 0.33
Diluted	$ 0.58	$ 0.61	$ 0.49	$ 0.37	$ (0.62)	$ 0.29	$ 0.26	$ 0.02	$ 2.04	$ (0.04)	$ 0.32
Stock options and stock awards excluded from EPS calculation because their inclusion would be anti-dilutive									1,103	3,508	1,427