Pension and Employee Benefit Plans - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions	$ 300,000	$ 29,000
Unfunded liability plans	10,900,000		$ 11,100,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated contribution to fund the pension plan during the reminder of the fiscal year	1,700,000
Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated contribution to fund the pension plan during the reminder of the fiscal year	$ 25,000