Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,678	$ 1,108	$ 2,634	$ 2,192
Interest cost	4,826	4,555	9,666	9,197
Expected return on plan assets	(5,434)	(5,657)	(10,878)	(11,331)
Amortization of prior service cost (credit)	16	8	32	16
Recognized actuarial (gain) loss	1,831	2,126	3,664	4,523
Settlement loss	0	2,401	0	2,443
Net periodic benefit cost	2,917	4,541	5,118	7,040
Postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	1
Interest cost	50	52	100	104
Amortization of prior service cost (credit)	(509)	(509)	(1,018)	(1,019)
Recognized actuarial (gain) loss	(96)	(80)	(192)	(160)
Net periodic benefit cost	$ (555)	$ (537)	$ (1,110)	$ (1,074)