Goodwill and Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangible assets	$ 1,000,000	$ 1,000,000	$ 1,000,000
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2018	2,000,000
2019	2,000,000
2020	2,000,000
2021	2,000,000
2022	$ 2,000,000
Weighted average remaining amortization period	21 years
Goodwill and intangible asset impairment	$ 0	$ 0	$ 0