Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Service cost component of defined benefit plan		$ 707	$ 643	$ 1,406	$ 1,279
Accounting Standards Update 2016-01 [Member]
Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings	$ 1,100