Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Net book value of intangible assets	$ 22,400,000	$ 10,400,000
Goodwill impairment charges	0	0
Finite-Lived Intangible Assets [Line Items]
Net book value of finite-lived intangible assets	19,900,000	$ 7,900,000
Impairment of Intangible Assets (Excluding Goodwill)	$ 0
Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets with defined useful lives, amortization period	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets with defined useful lives, amortization period	20 years