Pension and Postretirement Benefits - Summary of Weighted-Average Assumptions Used in Calculating Net Periodic Benefit (Credit) Cost (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted-average assumptions used to determine net periodic benefit (credit) loss:
Expected return on plan assets	7.25%	7.50%
Pension Plan and SERP Plan [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	3.99%	4.73%
Expected return on plan assets		7.50%
Weighted-average assumptions used to determine net periodic benefit (credit) loss:
Discount rate	4.73%	3.99%	4.73%
Expected return on plan assets	7.50%	7.50%	7.50%
Postretirement Plan [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	3.25%	3.25%
Expected return on plan assets	3.00%	4.00%
Weighted-average assumptions used to determine net periodic benefit (credit) loss:
Discount rate	3.25%	3.00%	3.45%
Expected return on plan assets	4.00%	4.00%	5.00%