Net Income (Loss) Per Share Attributable to Common Shareholders - Schedule of Computation of Basic and Diluted Net Income (Loss) per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic net income (loss) per common share calculation:
Net income (loss) attributable to common shareholders	$ 138,423	$ (53,699)	$ (48,408)	$ (50,711)	$ (38,380)	$ (28,300)	$ 36,316	$ (117,391)
Net income (loss) attributable to common shareholders - basic	$ 138,423			$ (50,711)			$ 36,316	$ (117,391)
Basic weighted-average common shares outstanding	54,829,057			47,391,988			53,380,123	46,709,388
Basic net income (loss) per common share	$ 2.52			$ (1.07)			$ 0.68	$ (2.51)
Diluted net income (loss) per common share calculation:
Net income (loss) attributable to common shareholders	$ 138,423	$ (53,699)	$ (48,408)	$ (50,711)	$ (38,380)	$ (28,300)	$ 36,316	$ (117,391)
Net income (loss) attributable to common shareholders - diluted	$ 138,423			$ (50,711)			$ 36,316	$ (117,391)
Basic weighted-average common shares outstanding	54,829,057			47,391,988			53,380,123	46,709,388
Effect of potentially dilutive securities:
Weighted-average shares used to compute diluted net income (loss) per common share	57,598,901			47,391,988			55,821,420	46,709,388
Diluted net income (loss) per common share	$ 2.40			$ (1.07)			$ 0.65	$ (2.51)
Stock Options [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities	2,612,354						2,326,824
Unvested Restricted Common Shares [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities	157,490						114,473