Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Retirement Benefits [Abstract]
Service cost	$ 2,379	$ 2,612	$ 4,769	$ 5,266
Interest cost	24,335	22,071	48,683	44,184
Expected return on plan assets	(38,507)	(38,516)	(77,034)	(77,104)
Amortization of prior service credit	(17)	(37)	(34)	(74)
Amortization of actuarial loss	7,746	9,935	15,495	19,894
Net periodic benefit income	$ (4,064)	$ (3,935)	$ (8,121)	$ (7,834)