Income Tax Expense - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 1,791,000	$ 26,000	$ 2,889,000	$ 26,000
Effective tax rate	(15.40%)	0.00%	(11.10%)	0.00%
Federal statutory income tax rate	21.00%		21.00%		35.00%
Tax Cuts and Jobs Act, accounting complete			false
Tax Cuts and Jobs Act, incomplete accounting, change in tax rate, adjustments	$ 0		$ 0

Indicates (true false) whether accounting for income tax effect of Tax Cuts and Jobs Act is complete.

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Amount of reasonable estimate for income tax expense (benefit) for remeasurement of deferred tax from change in tax rate pursuant to Tax Cuts and Jobs Act for which accounting for tax effect is incomplete.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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