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, 2020	Dec. 31, 2019	Dec. 31, 2018
Other changes in plan assets and benefit obligations recognized in other comprehensive loss:
Tax expense related to benefit plans included in other comprehensive income	$ 1,500	$ (5,500)	$ 2,100
Defined benefit pension plans
Net periodic benefit cost (credit):
Service cost	4,348	4,479	4,223
Interest cost	15,079	19,309	18,117
Expected return on plan assets	(19,694)	(21,714)	(22,508)
Amortization of prior service cost (credit)	303	64	29
Recognized actuarial loss (gain)	9,584	7,585	8,518
Settlement loss	0	0	3,248
Curtailment loss	50	92	739
Net periodic benefit cost	9,670	9,815	12,366
Other changes in plan assets and benefit obligations recognized in other comprehensive loss:
Net actuarial loss (gain)	12,624	28,740	(4,433)
Prior service cost	269	26	114
Amortization of prior service (cost) credit	(303)	(64)	(29)
Total recognized in other comprehensive (loss) income	12,590	28,702	(4,348)
Total recognized in net periodic benefit cost (credit) and other comprehensive loss	22,260	38,517	8,018
Postretirement benefit plans
Net periodic benefit cost (credit):
Service cost	1	1	1
Interest cost	139	201	208
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(2,038)	(2,038)	(2,037)
Recognized actuarial loss (gain)	(74)	(384)	(320)
Settlement loss	0	0	0
Curtailment loss	0	0	0
Net periodic benefit cost	(1,972)	(2,220)	(2,148)
Other changes in plan assets and benefit obligations recognized in other comprehensive loss:
Net actuarial loss (gain)	850	1,870	(276)
Prior service cost	0	0	0
Amortization of prior service (cost) credit	2,038	2,038	2,037
Total recognized in other comprehensive (loss) income	2,888	3,908	1,761
Total recognized in net periodic benefit cost (credit) and other comprehensive loss	$ 916	$ 1,688	$ (387)