Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Statutory federal corporate tax rate										35.00%
Estimate effects on deferred tax balances and recognized provisional amount included as component of provision for income taxes	$ 12,500									$ 12,509
Valuation allowance	1,337				$ 1,872					1,337	$ 1,872
Pre-tax loss	3,139	$ 3,351	$ (1,480)	$ 1,576	(5,822)	$ (327)	$ (30,607)	$ (8,374)		6,586	(45,130)	$ (2,572)
DTA related to net operating loss carryforwards	13,380				24,208					$ 13,380	24,208
DTA related to operating loss carryforwards expiration, description										do not expire until 2032 through 2036
AMT carryforwards	$ 1,991				$ 2,015					$ 1,991	$ 2,015
Scenario, Forecast
Income Taxes [Line Items]
Statutory federal corporate tax rate									21.00%