Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule Of Accounting Policies [Line Items]
Shares, non-dilutive	44,053	0
Reclassifications effect on net income	$ 0
Accounting Standards Update 2018-02 [Member]
Schedule Of Accounting Policies [Line Items]
Cumulative-effect adjustment from AOCI to increase retained earnings	$ 766,000