Pension and Profit Sharing Plans - Benefit Obligation Activity and Fair Value of Plan Assets and Statement of Funded Status (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 665,000	$ 622,000	$ 1,131,000
Actuarial loss (gain)	(4,688,000)	(6,098,000)
Employer contributions	500,000	500,000
Fair value of plan assets at December 31	15,787,000
Reconciliation of Benefit Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	16,002,000	15,581,000
Interest cost on projected benefit obligation	665,000	622,000
Actuarial loss (gain)	139,000	635,000
Benefits paid, including partial settlement of certain participant balances	(1,353,000)	(836,000)
Benefit obligation at December 31	15,453,000	16,002,000	15,581,000
Reconciliation of Fair Value of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	14,820,000	15,458,000
Actual return on plan assets	1,820,000	(302,000)
Employer contributions	500,000	500,000
Benefits paid, including partial settlement of certain participant balances	(1,353,000)	(836,000)
Fair value of plan assets at December 31	15,787,000	14,820,000	$ 15,458,000
Funded status	$ 334,000	$ (1,182,000)