Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 2,390	$ 2,654
Interest cost	24,348	22,113
Expected return on plan assets	(38,527)	(38,588)
Amortization of prior service credit	(17)	(37)
Amortization of actuarial loss	7,749	9,959
Net periodic benefit income	$ (4,057)	$ (3,899)