Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Federal income tax rate		21.00%	35.00%	35.00%
Federal net operating loss carryforwards expiration period start		2022
Federal net operating loss carryforwards expiration period end		2037
State operating loss carryforwards expiration period start		2019
State net operating loss carryingforwards period end		2037
Provisional decrease in federal income tax			$ 17,300,000
Net adjustment to deferred income tax benefit			17,300,000
U.S. transition tax	$ 200,000
Tax cuts and jobs act, provisional accounting for changes in income tax expense (benefit)		$ 17,500,000	17,300,000
Unrecognized tax benefits due to uncertain tax positions		6,000,000	$ 6,300,000	$ 6,300,000
Unrecognized tax benefits which would effect effective tax rate if recognized		500,000
Accrued interest and penalties related to uncertain tax positions		0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Federal Net operating loss carrying forward		299,000,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal Net operating loss carrying forward		$ 145,000,000
Foreign Jurisdiction | Earliest Tax Year
Operating Loss Carryforwards [Line Items]
Income tax year under examination		2006
Foreign Jurisdiction | Latest Tax Year
Operating Loss Carryforwards [Line Items]
Income tax year under examination		2017