Investments and Fair Value Measurements - Fair Value Measurements (Details) - USD ($) $ in Thousands		Jun. 30, 2020		Dec. 31, 2019
Fair Value Measurements [Abstract]
Available-for-sale securities		$ 254,144		$ 160,804
Recurring Basis [Member]
Fair Value Measurements [Abstract]
Money market funds	[1]	105,972		285,510
Total		360,116		446,314
Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		112,749	[2]	107,735	[3]
Recurring Basis [Member] | Corporate Debt Securities [Member] | Cash and Cash Equivalents [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities				4,000
Recurring Basis [Member] | Debt Securities Issued by U.S. Government Agencies [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities	[2]	141,395		53,069
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Fair Value Measurements [Abstract]
Money market funds	[1]	105,972		285,510
Total		105,972		285,510
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Measurements [Abstract]
Total		254,144		160,804
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		112,749	[2]	107,735	[3]
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities Issued by U.S. Government Agencies [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities	[2]	$ 141,395		$ 53,069

[1] Included in cash and cash equivalents on our condensed consolidated balance sheet

[2] Included in short-term investments on our condensed consolidated balance sheet

[3] At December 31, 2019, $4.0 million was included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet