Earnings Per Share - Components of Numerator and Denominator for Computation of Basic and Diluted Earnings per Share (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
Numerator:
Net income attributable to common shareholders - Basic									$ 37,513	$ 7,967	$ 4,418
Interest on Convertible Notes									694	3,383
Gain on derivative liability				$ (1,600)	$ 14,200	$ (7,100)	$ 3,600	$ (16,400)	(1,581)	(5,805)	9,901
Net income attributable to common shareholders - Diluted									$ 36,626	$ 5,545	$ 4,418
Denominator:
Weighted average common shares - Basic (shares)									35,018	32,132	31,514
Effective of diluted shares:
Share-based awards (shares)									425	593	648
Convertible Notes (shares)									723	3,521	0
Weighted average common shares - Diluted (shares)									36,166	36,246	32,162
Net income per share attributable to common shareholders - Basic (usd per share)	$ 0.78	$ 0.19	$ 0.14	$ (0.06)	$ (0.24)	$ 0.44	$ (0.54)	$ 0.60	$ 1.07	$ 0.25	$ 0.14
Net income per share attributable to common shareholders - Diluted (usd per share)	$ 0.77	$ 0.19	$ 0.13	$ (0.08)	$ (0.24)	$ 0.22	$ (0.54)	$ 0.09	$ 1.01	$ 0.15	$ 0.14