Summary of Significant Accounting Policies - Reconciliation of Net Income (Loss) and Weighted Average Shares used in Computing Basic and Diluted Net Income (Loss) Per Share (Detail) - 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
Basic net loss per share:
Net loss applicable to common shares									$ (29,136)	$ (2,834)	$ (4,060)
Weighted average common shares outstanding									13,623	12,150	11,505
Basic net loss per share of common stock	$ (1.82)	$ (0.01)	$ (0.06)	$ (0.21)	$ (0.28)	$ 0.00	$ 0.11	$ (0.06)	$ (2.14)	$ (0.23)	$ (0.35)
Diluted net loss per share:
Net loss applicable to common shares									$ (29,136)	$ (2,834)	$ (4,060)
Weighted average common shares outstanding									13,623	12,150	11,505
Dilutive effects of stock options and restricted stock awards									0	0	0
Weighted average common shares, assuming dilutive effect of stock options									13,623	12,150	11,505
Diluted net loss per share of common stock	$ (1.82)	$ (0.01)	$ (0.06)	$ (0.21)	$ (0.28)	$ 0.00	$ 0.09	$ (0.06)	$ (2.14)	$ (0.23)	$ (0.35)