Summary of Significant Accounting Policies - Summary of Reconciliation of Amounts in Previously Reported Consolidated Financial Statements - Statement of Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Net loss	$ 36,490	$ 3,998	$ (19,036)	$ (2,626)	$ (13,122)	$ (16,694)	$ 11,494	$ 26,847	$ 18,826	$ 8,525	$ (206,735)
Total Comprehensive loss											(206,735)
As Reported [Member]
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Net loss											(203,806)
Total Comprehensive loss											(203,806)
Adjustment [Member]
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Net loss											(2,929)
Total Comprehensive loss											$ (2,929)