Income Tax - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Percentage of annual effective income tax rate	0.00%
Pre-tax book income	$ 18,826,000	$ 8,525,000	$ (206,189,000)
U.S. federal tax loss carryforwards ("NOL")	667,000,000
Valuation allowance	208,324,000	213,800,000	359,098,000
Reserve for uncertain tax positions	0	$ 0	$ 0
Federal [Member]
Income Tax [Line Items]
U.S. federal tax loss carryforwards ("NOL")	$ 667,000,000
Tax loss carryforwards expiration year	2034