Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes Disclosure [Line Items]
Deferred tax assets, valuation allowance		$ 54,829,000
Reduction in net deferred tax assets before valuation allowance due to enactment of Tax Legislation		28,163,000
Offsetting change in valuation allowance impact to net income due to enactment of tax legislation		0
Foreign investments benefit		0	$ 0
Decreased (increased) income tax benefit		8,569,000	(323,000)
Net operating loss carryforwards		$ 59,536,000	$ 51,722,000
Income tax refund received	$ 37,397,000
Net operating losses carry forwards, expiration year		2037	2036
Claim of bonus tax depreciation		$ 0	$ 0	$ 29,221,000	$ 61,781,000
Uncertain tax positions		0		$ 153,000
Uncertain tax positions reduced			$ 0
Tax Years 2012 Through 2014
Income Taxes Disclosure [Line Items]
Income tax refund claimed		$ 2,206,000