Employee Benefit Plans - Components of Net Periodic Defined Benefit Cost (Income) (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 506,000	$ 592,000
Expected return on plan assets	(689,000)	(735,000)
Recognized actuarial (gains) losses	394,000	431,000
Total	211,000	288,000	$ 865,000
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	20,000	24,000
Amortization of prior service credit		(135,000)
Recognized actuarial (gains) losses	(54,000)	(38,000)
Total	$ (34,000)	$ (149,000)	$ (597,000)