Employee Stock Ownership Plans - Summary of Stock Option Outstanding (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning Balance	1,702,337
Number of Shares, Granted	382,033
Number of Shares, Forfeited	(20,796)
Number of Shares, Ending Balance	2,063,574	1,702,337
Number of Shares, Exercisable at December 31, 2016	707,260
Number of Shares, Expected to vest at December 31, 2016	1,190,710
Weighted Average Grant Date Fair Value Per Share, Beginning Balance	$ 9.60
Weighted Average Grant Date Fair Value Per Share, Granted	2.16	$ 3.82	$ 5.37
Weighted Average Grant Date Fair Value Per Share, Forfeited	6.62
Weighted Average Grant Date Fair Value Per Share, Ending Balance	8.26	9.60
Weighted Average Grant Date Fair Value Per Share, Exercisable at December 31, 2016	17.10
Weighted Average Grant Date Fair Value Per Share, Expected to vest at December 31, 2016	3.58
Weighted Average Exercise Price Per Share, Beginning Balance	13.47
Weighted Average Exercise Price Per Share, Granted	4.30
Weighted Average Exercise Price Per Share, Forfeited	10.58
Weighted Average Exercise Price Per Share, Ending Balance	11.80	$ 13.47
Weighted Average Exercise Price Per Share, Exercisable at December 31, 2016	19.81
Weighted Average Exercise Price Per Share, Expected to vest at December 31, 2016	$ 6.99
Weighted Average Remaining Contractual Term, Beginning Balance	8 years 3 months 18 days	9 years 29 days
Weighted Average Remaining Contractual Term, Exercisable at December 31, 2016	7 years 8 months 5 days
Weighted Average Remaining Contractual Term, Expected to vest at December 31, 2016	8 years 8 months 1 day
Aggregate Intrinsic Value, Beginning Balance	$ 6,152,000
Aggregate Intrinsic Value, Exercised			$ 4,816,500
Aggregate Intrinsic Value, Ending Balance	36,326,000	$ 6,152,000
Aggregate Intrinsic Value, Expected to vest at December 31, 2016	$ 31,473,000