Defined Benefit Pension Plan and Postretirement Benefits - Net Periodic Benefit Cost and Other Accumulated Comprehensive Income for Pension Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Service cost	$ 433	$ 387	$ 392
Interest cost	135	104	137
Recognized actuarial (gains)	(41)	(50)	(60)
Net periodic benefit cost	527	441	469
Unrealized net actuarial (gains), net of tax	(1,029)	(1,008)	(1,150)
Total amount recognized in net periodic benefit cost and other accumulated comprehensive income (loss)	$ (502)	$ (567)	$ (681)