Stock Based Compensation - Summary of Stock Option Transactions under Company's Stock Incentive Plans (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Outstanding, Beginning Balance	1,202,801	945,584	859,443
Shares, Granted	590,200	339,975	235,675
Shares, Exercised	0	0	0
Shares, Forfeited	(68,330)	(82,758)	(149,534)
Shares Outstanding, Ending Balance	1,724,671	1,202,801	945,584
Shares Vested and unvested options expected to vest as of December 31, 2016	1,724,671
Weighted Average Exercise Price, Beginning Balance	$ 17.61	$ 23.27	$ 26.58
Weighted Average Exercise Price, Granted	2.30	3.51	10.06
Weighted Average Exercise Price, Exercised	0	0	0
Weighted Average Exercise Price, Forfeited	22.17	24.37	21.51
Weighted Average Exercise Price, Ending Balance	12.19	$ 17.61	$ 23.27
Weighted Average Exercise Price, Vested and unvested options expected to vest as of December 31, 2016	$ 12.19