Summary of Significant Accounting Policies - Cash, Cash Equivalents and Marketable Securities and Restricted Cash (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Interest income	$ 3,287,000	$ 939,000	$ 443,000
Restricted cash	70,087,000	0
Cash and Cash Equivalents
Cash and Cash Equivalents [Line Items]
Interest income	3,100,000	$ 900,000
Restricted Cash
Cash and Cash Equivalents [Line Items]
Interest income	$ 100,000