Summary of Significant Accounting Policies Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents and Marketable Securities [Abstract]
Cash and cash equivalents	$ 23,620	$ 5,057	$ 31,360	$ 29,078
Restricted cash	2,015	2,047	1,967	1,851
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 25,635	$ 7,104	$ 33,327	$ 30,929