Marketable Securities - Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized gains	$ 60
Cost
Debt Securities, Available-for-sale [Line Items]
Total Available-for-sale Securities	39,033	$ 64,138
Cost | Certificates of deposit | Level 1
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	251	250
Marketable Securities with unrecognized losses for more than 12 months	0	3,861
Marketable Securities with unrecognized gains	1,799	0
Total Available-for-sale Securities	2,050	4,111
Cost | U.S. Treasury and agency notes | Level 2
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	6,485	3,112
Marketable Securities with unrecognized losses for more than 12 months	0	23,564
Marketable Securities with unrecognized gains	14,413	3
Total Available-for-sale Securities	20,898	26,679
Cost | Corporate notes | Level 2
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	1,004	13,696
Marketable Securities with unrecognized losses for more than 12 months	0	12,542
Marketable Securities with unrecognized gains	13,082	0
Total Available-for-sale Securities	14,086	26,238
Cost | Municipal notes | Level 2
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	0	2,994
Marketable Securities with unrecognized losses for more than 12 months	0	4,116
Marketable Securities with unrecognized gains	1,999	0
Total Available-for-sale Securities	1,999	7,110
Estimated Fair Value
Debt Securities, Available-for-sale [Line Items]
Total Available-for-sale Securities	39,084	63,749
Estimated Fair Value | Certificates of deposit | Level 1
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	250	248
Marketable Securities with unrecognized losses for more than 12 months	0	3,812
Marketable Securities with unrecognized gains	1,806	0
Total Available-for-sale Securities	2,056	4,060
Estimated Fair Value | U.S. Treasury and agency notes | Level 2
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	6,479	3,105
Marketable Securities with unrecognized losses for more than 12 months	0	23,415
Marketable Securities with unrecognized gains	14,434	4
Total Available-for-sale Securities	20,913	26,524
Estimated Fair Value | Corporate notes | Level 2
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	1,002	13,665
Marketable Securities with unrecognized losses for more than 12 months	0	12,431
Marketable Securities with unrecognized gains	13,106	0
Total Available-for-sale Securities	14,108	26,096
Estimated Fair Value | Municipal notes | Level 2
Debt Securities, Available-for-sale [Line Items]
Marketable Securities with unrecognized losses for less than 12 months	0	2,982
Marketable Securities with unrecognized losses for more than 12 months	0	4,087
Marketable Securities with unrecognized gains	2,007	0
Total Available-for-sale Securities	$ 2,007	$ 7,069