Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments, Owned, Federal Income Tax Note [Line Items]
Effective income tax rate reconciliation at federal statutory income tax rate	21.00%	35.00%
Income Tax Expense (Benefit)	$ 4,846	$ 8,434
Effective Income Tax Rate Reconciliation, Percent	18.60%	29.50%