Income Tax - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Examination [Line Items]
Percentage of annual effective income tax rate		0.00%
Valuation allowance		$ 213,800,000	$ 359,098,000	$ 287,786,000
U.S. federal tax loss carryforwards ("NOL")		$ 546,000,000
Tax loss carryforwards expiration year		2034
U.S. statutory tax rate		35.00%	35.00%	35.00%
Tax cuts and jobs act of 2017 change in tax rate reduction of tax benefit		$ 142,000,000
Tax cuts and jobs act of 2017 change in tax rate reversal of valuation allowance		142,000,000
Tax cuts and jobs act of 2017 change in tax rate impact to income tax provision		0
Reserve for uncertain tax positions		$ 0	$ 0	$ 0
Scenario, Forecast [Member]
Income Tax Examination [Line Items]
U.S. statutory tax rate	21.00%