Income Taxes - Expiration of Loss and Tax Credit Carryforwards (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Operating Loss and Tax Credit Carryforward [Line Items]
Loss carryforwards	$ 639,147
Tax credit carryforwards	60,591
Period of Expiration 2017 - 2021
Operating Loss and Tax Credit Carryforward [Line Items]
Loss carryforwards	52,614
Tax credit carryforwards	1,578
Period of Expiration Thereafter
Operating Loss and Tax Credit Carryforward [Line Items]
Loss carryforwards	321,859
Tax credit carryforwards	54,376
No Expiration Date
Operating Loss and Tax Credit Carryforward [Line Items]
Loss carryforwards	264,674
Tax credit carryforwards	$ 4,637