Employee Benefit Plans - Pension Plans with Accumulated Benefit Obligation in Excess of Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined benefit plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 544,581	$ 654,536
Projected benefit obligation	544,581	654,536	$ 625,535
Fair value of plan assets	361,891	464,441	412,459
SERPs
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	16,985	23,691
Projected benefit obligation	16,985	23,691	21,260
Fair value of plan assets	$ 0	$ 0	$ 0