Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale securities
Fair Value Measurements
Unrealized losses	$ 23,200
Recurring
Financial Assets:
Total financial assets	367,499	$ 401,542
Recurring | Money market deposits
Financial Assets:
Total financial assets	35,818	22,477
Recurring | U.S. Treasury securities
Financial Assets:
Total financial assets	249,314	293,157
Recurring | Municipal securities
Financial Assets:
Total financial assets	82,367	85,908
Recurring | Level 1
Financial Assets:
Total financial assets	285,132	315,634
Recurring | Level 1 | Money market deposits
Financial Assets:
Total financial assets	35,818	22,477
Recurring | Level 1 | U.S. Treasury securities
Financial Assets:
Total financial assets	249,314	293,157
Recurring | Level 2
Financial Assets:
Total financial assets	82,367	85,908
Recurring | Level 2 | Municipal securities
Financial Assets:
Total financial assets	$ 82,367	85,908
Contingent consideration | Evercord
Liabilities:
Total consideration		$ 4,700