Benefit Plans - Net Periodic Benefit Cost (Increase) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Amortization of lump sum pension distribution	$ 1,300
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	$ 0	$ 0
Interest cost	1,137	1,271	1,273
Return on plan assets	(2,530)	(3,463)	(3,167)
Amortization of net gain (loss)	774	441	1,352
Amortization of lump sum pension distribution	0	1,336	0
Amortization of unrecognized prior service cost	0	0	0
Net periodic benefit cost (increase)	(619)	(415)	(542)
Post-retirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	168	169	240
Interest cost	1,122	1,087	981
Return on plan assets	0	0	0
Amortization of net gain (loss)	1	(204)	15
Amortization of lump sum pension distribution	0	0	0
Amortization of unrecognized prior service cost	(1)	(4)	(4)
Net periodic benefit cost (increase)	$ 1,290	$ 1,048	$ 1,232