Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Significant Accounting Policies [Line Items]        
Accumulated deficit $ 338,093 $ 296,650    
Restricted cash includes into cash, cash equivalents and restricted cash $ 91,889 80,617 $ 63,824 $ 48,162
Accounting Standards Update 2016-18        
Significant Accounting Policies [Line Items]        
Restricted cash includes into cash, cash equivalents and restricted cash   $ 1,400 $ 1,400 $ 200
Adoption of new accounting pronouncements, Description On January 1, 2018, the Company adopted two new accounting standards issued by the FASB that clarify presentation and classification in the statement of cash flows on a retrospective basis.