Summary of Significant Accounting Policies - Intangible Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 16,723
Accumulated amortization	0
Net balance	16,723
Future Amortization Expense:
2018	1,600
2019	1,600
2020	1,600
2021	1,600
2022	$ 1,600
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Useful life of intangible assets	15 years
Gross amount	$ 11,622
Accumulated amortization	0
Net balance	$ 11,622
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Useful life of intangible assets	5 years
Gross amount	$ 900
Accumulated amortization	0
Net balance	$ 900
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Useful life of intangible assets	7 years
Gross amount	$ 4,201
Accumulated amortization	0
Net balance	$ 4,201