Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Income Taxes [Line Items]
Corporate tax rate	21.00%	35.00%	21.00%	35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ 12,800
Tax cuts and jobs Act, increased tax provision on undistributed and previously untaxed post-1986 earnings and profits of the specified foreign corporation				$ 3,300
Impact on assets and liabilities due to change in accounting principle		$ (677)
Income tax (benefit) provision	23.40%	24.70%
Accounting Standards Update 2016-06 [Member] | Other Assets [Member]
Income Taxes [Line Items]
Impact on assets and liabilities due to change in accounting principle					$ 5,700
Accounting Standards Update 2016-06 [Member] | Deferred tax liablities [Member]
Income Taxes [Line Items]
Impact on assets and liabilities due to change in accounting principle					5,000
Accounting Standards Update 2016-06 [Member] | accumulated deficit [Member]
Income Taxes [Line Items]
Impact on assets and liabilities due to change in accounting principle					$ 700
Latest Tax Year
Income Taxes [Line Items]
Net operating loss and business tax credit carry forwards expiration date			at various dates through December 2038
State
Income Taxes [Line Items]
Business tax credits carry forwards			$ 2,800
United States
Income Taxes [Line Items]
Business tax credits carry forwards			$ 400