Summary of Significant Accounting Policies - Summary of Reconciliation of Amounts in Previously Reported Consolidated Financial Statements - Statement of Stockholders' Equity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Accumulated deficit	$ (1,396,145)	$ (1,404,670)	$ (1,197,935)	$ (236,144)
Total stockholders' equity	$ 572,354	556,607	633,374	1,155,912
As Reported [Member]
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Accumulated deficit		(1,414,561)	(1,210,755)	(239,345)
Total stockholders' equity		546,716	620,554	1,152,711
Adjustment [Member]
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Accumulated deficit		9,891	12,820	3,201
Total stockholders' equity		$ 9,891	$ 12,820	$ 3,201