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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Accumulated deficit	$ (1,377,319)	$ (1,396,145)	$ (1,404,670)
Total stockholders' equity	$ 687,486	$ 572,354	556,607	$ 633,374
As Reported [Member]
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Accumulated deficit			(1,414,561)
Total stockholders' equity			546,716
Adjustment [Member]
Quantifying Misstatement In Current Year Financial Statements [Line Items]
Accumulated deficit			9,891
Total stockholders' equity			$ 9,891