Employee Benefit Plans (RELS Pension Plan Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Contributions to settled benefit benefit pension plan		$ 12,700
Impairment loss on investment in affiliates		3,811	$ 23,431	$ 0
Other liabilities		165,176	132,043
Accumulated other comprehensive loss		93,691	$ 122,418
RELS LLC [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Contributions to settled benefit benefit pension plan	$ 13,500
Impairment loss on investment in affiliates		$ 5,100
Other liabilities	9,200
Accumulated other comprehensive loss	$ 1,800