Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective tax rate	12.20%	25.40%	18.60%	26.20%
Corporate tax rate			21.00%		35.00%
Expects repatriate			$ 100,000,000
Provisional transition tax obligation	$ 400,000		19,000,000		$ 19,400,000
Income tax expense	$ 400,000		$ 19,000,000		19,400,000
Measurement-period adjustment reduction of rate	0.40%		4.90%
Additional income tax expense	$ 1,900,000
Increase in effective tax rate			1.80%
Deferred income tax benefit					$ 4,500,000
Favorable measurement-period adjustment			$ 5,200,000
Tax Cuts And Jobs Act Of 2017 Income Tax Expense Benefit			$ 9,700,000
Deduction percent of qualified property			100.00%
Additional bonus depreciation			20.00%
Addition in valuation allowance	0		$ 0
Change in valuation allowance	$ 0		$ 0