Share-based Compensation - Share-based Compensation Plan - Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Options
Options, outstanding beginning balance (in shares)			7,008,403
Options, granted (in shares)	263,500	145,000	1,718,950	997,975
Options, exercised (in shares)			(12,852)
Options, forfeited (in shares)			(20,960)
Options, expired (in shares)			(21,336)
Options, outstanding ending balance (in shares)	8,672,205		8,672,205		7,008,403
Options, vested and expected to vest ending balance (in shares)	8,194,918		8,194,918
Options, Vested (in shares)			4,500,202
Weighted Average Exercise Price
Weighted average exercise price, outstanding beginning balance (in dollars per share)			$ 23.34
Weighted average exercise price, granted (in dollars per share)			11.87
Weighted average exercise price, exercised (in dollars per share)			11.76
Weighted average exercise price, forfeited (in dollars per share)			11.44
Weighted average exercise price, expired (in dollars per share)			33.61
Weighted average exercise price, outstanding ending balance (in dollars per share)	$ 21.09		21.09		$ 23.34
Weighted average exercise price, vested and expected to vest, ending balance (in dollars per share)	21.50		21.50
Weighted Average Exercise Price, vested (in dollars per shares)	$ 26.35		$ 26.35
Options, Additional Disclosures
Weighted average remaining contractual term, outstanding (in years)			7 years 4 months 13 days		7 years 2 months 26 days
Weighted average remaining contractual term, vested and expected to vest (in years)			7 years 3 months 7 days
Weighted Average Remaining Contractual Term, vested (in years)			6 years 14 days
Aggregate intrinsic value, outstanding	$ 2,426		$ 2,426		$ 11,901
Aggregate intrinsic value, vested and expected to vest, ending balance	2,407		2,407
Aggregate intrinsic value, vested	$ 2,254		$ 2,254