Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
U.S. federal corporate tax rate		34.90%	35.00%	35.00%
Tax cuts and jobs act of 2017, accounting complete [true false]		false
Change in net deferred tax expense (benefit)		$ (75,200)
Operating loss carryforwards		1,388	$ 1,399
State incentive tax credit carryforwards		3,411	1,694
Valuation allowances		1,681	456
Unrecognized tax benefits		3,827	1,832	$ 1,139
Potential increase (decrease) in income tax provision		2,800	$ 1,200
Income tax interest and penalty recognized		3
Tax settlement, amount		10,000
State [Member] | Net Operating Losses [Member]
Income Taxes [Line Items]
Valuation allowances		100
State [Member] | Tax Incentive Credit Carryforwards [Member]
Income Taxes [Line Items]
Valuation allowances		$ 1,600
Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date		Dec. 31, 2018
Tax credit carryforward, expiration date		Dec. 31, 2019
Possible reduction in unrecognized tax benefits resulting from audit settlements		$ 1,000
Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date		Dec. 31, 2037
Tax credit carryforward, expiration date		Dec. 31, 2022
Possible increase in unrecognized tax benefits resulting from audit settlements		$ 1,000
Scenario, Previously Reported [Member]
Income Taxes [Line Items]
U.S. federal corporate tax rate		35.00%
Scenario, Forecast [Member]
Income Taxes [Line Items]
U.S. federal corporate tax rate	21.00%