Income Taxes - Schedule of Net Operating Loss Carryforwards (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 615,951
Net operating loss carryforwards that will not be available to offset	242,000
2018
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	11,730
2019 to 2021
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	207,237
2022 to 2024
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	51,121
2025 to 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	22,430
2031 to 2033
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	767
Thereafter
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	322,666
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	311,332
Net operating loss carryforwards that will not be available to offset	241,800
Federal | 2018
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
Federal | 2019 to 2021
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	190,125
Federal | 2022 to 2024
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	46,827
Federal | 2025 to 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	13,005
Federal | 2031 to 2033
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
Federal | Thereafter
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	61,375
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	20,150
Net operating loss carryforwards that will not be available to offset	200
State | 2018
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
State | 2019 to 2021
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	474
State | 2022 to 2024
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
State | 2025 to 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
State | 2031 to 2033
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	767
State | Thereafter
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	18,909
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	284,469
Foreign | 2018
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	11,730
Foreign | 2019 to 2021
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	16,638
Foreign | 2022 to 2024
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	4,294
Foreign | 2025 to 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	9,425
Foreign | 2031 to 2033
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
Foreign | Thereafter
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 242,382