Income Taxes - Additional Information (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Dec. 22, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense		$ 6,245,000	$ 7,605,000
Effective tax rates on pre-tax income		15.32%	22.23%
Federal statutory tax rate		21.00%		35.00%
Restatement of deferred tax liability due to change in tax rate				$ 7,650,000
Change in deferred tax assets and liabilities related to reclassification from accumulated other comprehensive income to retained earnings	$ 5,759,000