Cash, Cash Equivalents, Marketable Securities, and Restricted Cash - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents	$ 123,231,000	$ 142,837,000	$ 96,349,000
Available-for-sale debt securities	215,642,000	309,903,000
Realized gain (loss) on debt securities	0	0
Fair value of available-for-sale debt securities in unrealized loss positions	99,500,000	42,600,000
Restricted cash	2,662,000		2,579,000
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 125,893,000	$ 146,341,000	$ 98,928,000	$ 82,375,000