Fair Value Measurements (Details) - USD ($) $ in Thousands		Mar. 31, 2022		Dec. 31, 2021		Mar. 31, 2021
0.125% Notes [Member]
Fair Value Measurements [Abstract]
Interest rate on convertible senior notes		0.125%		0.125%		0.125%
0% Notes [Member]
Fair Value Measurements [Abstract]
Interest rate on convertible senior notes		0.00%		0.00%
Significant Other Observable Inputs (Level 2) [Member] | 0.125% Notes [Member]
Fair Value Measurements [Abstract]
Fair value of convertible notes		$ 494,400
Significant Other Observable Inputs (Level 2) [Member] | 0% Notes [Member]
Fair Value Measurements [Abstract]
Fair value of convertible notes		595,400
Recurring Basis [Member]
Fair Value Measurements [Abstract]
Cash equivalents	[1]	407,399		$ 541,199
Total		1,967,666		1,807,528
Recurring Basis [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment	[2]	11,131		14,330
Recurring Basis [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment	[2]	438		3,875
Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		754,008	[3]	764,059	[4]
Recurring Basis [Member] | Corporate Debt Securities [Member] | Cash and Cash Equivalents [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		13,500
Recurring Basis [Member] | Debt Securities Issued by U.S. Government Agencies [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities	[4]	105,228		120,868
Recurring Basis [Member] | Debt Securities Issued by U.S. Government Agencies [Member] | Cash and Cash Equivalents [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities				2,300
Recurring Basis [Member] | Debt Securities Issued by the U.S. Treasury [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		490,792	[5]	182,634	[4]
Recurring Basis [Member] | Debt Securities Issued by the U.S. Treasury [Member] | Cash and Cash Equivalents [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		15,000
Recurring Basis [Member] | Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		192,350	[6]	174,464	[7]
Recurring Basis [Member] | Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member] | Cash and Cash Equivalents [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		10,300
Recurring Basis [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities	[4]	6,320		6,099
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Fair Value Measurements [Abstract]
Cash equivalents		407,399		541,199
Total		898,629		727,708
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment		0		0
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment		438		3,875
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities Issued by U.S. Government Agencies [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities Issued by the U.S. Treasury [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		490,792		182,634
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Measurements [Abstract]
Cash equivalents		0		0
Total		1,057,906		1,065,490
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment		0		0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment		0		0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		754,008		764,059
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		105,228		120,868
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities Issued by the U.S. Treasury [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		192,350		174,464
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		6,320		6,099
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Abstract]
Cash equivalents		0		0
Total		11,131		14,330
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment		11,131		14,330
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment		0		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities Issued by U.S. Government Agencies [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities Issued by the U.S. Treasury [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		0		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		$ 0		$ 0

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

[2] Included in other current assets on our condensed consolidated balance sheet.

[3] $13.5 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.

[4] Included in short-term investments.

[5] $15.0 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.

[6] $10.3 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.

[7] $2.3 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.