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								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic net income (loss) per common share calculation:
Net income (loss) attributable to common shareholders	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 66,858	$ (164,981)	$ (68,357)
Net income (loss) attributable to common shareholders - basic									$ 66,858	$ (164,981)	$ (68,357)
Basic weighted-average common shares outstanding	57,395,839	54,829,057	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	54,392,304	47,964,368	40,057,365
Basic net income (loss) per common share	$ 0.53	$ 2.52	$ (1.01)	$ (0.93)	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 1.23	$ (3.44)	$ (1.71)
Diluted net income (loss) per common share calculation:
Net income (loss) attributable to common shareholders	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 66,858	$ (164,981)	$ (68,357)
Net income (loss) attributable to common shareholders - diluted									$ 66,858	$ (164,981)	$ (68,357)
Basic weighted-average common shares outstanding	57,395,839	54,829,057	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	54,392,304	47,964,368	40,057,365
Effect of potentially dilutive securities:
Weighted-average shares used to compute diluted net income (loss) per common share	60,233,927	57,598,901	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	56,932,798	47,964,368	40,057,365
Diluted net income (loss) per common share	$ 0.51	$ 2.40	$ (1.01)	$ (0.93)	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 1.17	$ (3.44)	$ (1.71)
Outstanding Options [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities									2,406,962
Unvested Restricted Common Shares [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities									133,532