Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Historical compounded return on plan assets, minimum (in years)	10 years
Historical compounded return on plan assets, maximum (in years)	15 years
Defined contribution plans	$ 19,000	$ 17,800	$ 17,400
Cash Surrender Value of Life Insurance	45,400	34,400
Deferred compensation	68,300	53,600
Deferred compensation, non current	65,319	47,008
Deferred compensation, current	3,000	6,600
Rabbi Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets held in trust, current	52,100	45,000
Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets held in trust, current	6,700	10,600
TVN [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plans	4,800	4,400	$ 2,100
Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Company contributions	1,417	10,000
Expected contributing cash	2,700
Expected benefit payments to SERP in 2018	6,584
Net actuarial loss during 2018	2,600
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Company contributions	4,264	$ 5,724
Expected benefit payments to SERP in 2018	12,929
Net actuarial loss during 2018	$ 3,000