Variable Interest Entities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
DEQPS
Variable Interest Entity [Line Items]
Purchased shared services from VIE	$ 300,000	$ 400,000
DES
Variable Interest Entity [Line Items]
Purchased shared services from VIE	$ 12,200,000
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
Services provided by Affiliates | Affiliates | DES
Variable Interest Entity [Line Items]
Amounts due to VIE	$ 5,000,000