Variable Interest Entities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
DEQPS
Variable Interest Entity [Line Items]
Purchased shared services from VIE	$ 300,000	$ 400,000	$ 900,000	$ 1,100,000
DES
Variable Interest Entity [Line Items]
Purchased shared services from VIE	11,600,000		$ 36,700,000
Affiliates
Variable Interest Entity [Line Items]
Service agreement effective date with DES			2018-01
Services provided by Affiliates | Affiliates | DEQPS | Maximum
Variable Interest Entity [Line Items]
Amounts due to VIE	100,000		$ 100,000		$ 100,000
Services provided by Affiliates | Affiliates | DES
Variable Interest Entity [Line Items]
Amounts due to VIE	$ 3,700,000		$ 3,700,000