Fair Value Measurements (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value Measurements
Fair value, transfers between Level I and Level II assets	$ 0
Recurring
Financial Assets:
Total financial assets	192,366	$ 134,000
Recurring | Money market deposits
Financial Assets:
Total financial assets	5,666	26,539
Recurring | U.S. Treasury securities
Financial Assets:
Total financial assets	131,635	75,685
Recurring | U.S. agency securities
Financial Assets:
Total financial assets	7,000	12,891
Recurring | Municipal securities
Financial Assets:
Total financial assets	48,065	18,885
Recurring | Level 1
Financial Assets:
Total financial assets	137,301	102,224
Recurring | Level 1 | Money market deposits
Financial Assets:
Total financial assets	5,666	26,539
Recurring | Level 1 | U.S. Treasury securities
Financial Assets:
Total financial assets	131,635	75,685
Recurring | Level 2
Financial Assets:
Total financial assets	55,065	31,776
Recurring | Level 2 | U.S. agency securities
Financial Assets:
Total financial assets	7,000	12,891
Recurring | Level 2 | Municipal securities
Financial Assets:
Total financial assets	48,065	$ 18,885
Contingent consideration | Evercord
Liabilities:
Total consideration	$ 4,700