Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net loss available to common stockholders	$ (13,262)	$ (88,520)	$ (546)	$ (2,169)	$ (2,925)	$ (1,325)	$ 27	$ (528)	$ (104,497)	$ (4,751)	$ (5,120)
Denominator:
Denominator for basic calculation	92,526	92,029	91,689	91,643	91,175	90,774	89,987	89,434	92,017	90,340	88,477
Denominator for diluted calculation	92,526	92,029	91,689	91,643	91,175	90,774	93,447	89,434	92,017	90,340	88,477
Net loss per share:
Basic	$ (0.14)	$ (0.96)	$ (0.01)	$ (0.02)	$ (0.03)	$ (0.01)	$ 0.00	$ (0.01)	$ (1.14)	$ (0.05)	$ (0.06)
Diluted	$ (0.14)	$ (0.96)	$ (0.01)	$ (0.02)	$ (0.03)	$ (0.01)	$ 0.00	$ (0.01)	$ (1.14)	$ (0.05)	$ (0.06)