Employee Benefit Plans - Summary of Components of Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Tax (benefit) expense related to benefit plans included in other comprehensive income	$ 1,200	$ 1,100	$ (17,800)
Defined benefit pension plans
Net periodic benefit cost:
Service cost	5,557	6,105	7,515
Interest cost	24,526	26,007	27,708
Expected return on plan assets	(25,726)	(29,850)	(31,833)
Amortization of prior service cost (credit)	461	(465)	(1,037)
Recognized actuarial loss	6,994	15,168	15,771
Settlement loss	1,772	6,453	0
Curtailment loss (gain)	415	(8,639)	0
Net periodic benefit cost	13,999	14,779	18,124
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial (gain) loss	(1,531)	(8,813)	48,502
Prior service cost	505	8,691	20
Amortization of prior service (cost) credit	(461)	465	1,037
Total recognized in other comprehensive income	(1,487)	343	49,559
Total recognized in net periodic benefit cost and other comprehensive income	12,512	15,122	67,683
Postretirement benefit plans
Net periodic benefit cost:
Service cost	52	54	67
Interest cost	1,143	1,194	1,377
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	0	0	0
Recognized actuarial loss	148	148	17
Settlement loss	0	0	0
Curtailment loss (gain)	0	0	0
Net periodic benefit cost	1,343	1,396	1,461
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial (gain) loss	(1,833)	(3,130)	(2,205)
Prior service cost	0	0	0
Amortization of prior service (cost) credit	0	0	0
Total recognized in other comprehensive income	(1,833)	(3,130)	(2,205)
Total recognized in net periodic benefit cost and other comprehensive income	$ (490)	$ (1,734)	$ (744)