Income Taxes - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017 USD ($) Tax_Positions	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Income Tax Contingency [Line Items]
Deferred tax assets, liability		$ 1,900,000
Valuation allowance		3,096,000	$ 4,061,000
Income tax expense (benefit)		$ 46,791,000	34,983,000	$ 28,689,000
Unrecognized tax benefits number of tax matters | Tax_Positions		0
Unrecognized tax benefits related to identified uncertain tax positions		$ 0
Accounting Standards Update 2016-09 [Member]
Income Tax Contingency [Line Items]
Income tax expense (benefit)		$ (1,500,000)	$ (1,700,000)
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Statutory tax rate, percentage	21.00%
Earliest Tax Year [Member] | Federal Tax Jurisdiction [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2013
Latest Tax Year [Member] | Federal Tax Jurisdiction [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2016