Organization and Significant Accounting Policies, Fair Value Measurements (Details) - USD ($) $ in Thousands		Dec. 31, 2021		Apr. 30, 2021	Dec. 31, 2020		Dec. 31, 2019
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%			0.00%
Recurring Basis [Member]
Fair Value Measurements [Abstract]
Cash equivalents	[1]	$ 541,199			$ 221,125
Total		1,807,528			1,745,363
Recurring Basis [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment	[2]	14,330
Recurring Basis [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment	[2]	3,875			2,031
Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		764,059	[3]		846,315	[4]
Recurring Basis [Member] | Corporate Debt Securities [Member] | Cash and Cash Equivalents [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		2,300			10,000
Recurring Basis [Member] | Debt Securities Issued by U.S. Government Agencies [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities	[3]	120,868			174,861
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					17,500
Recurring Basis [Member] | Debt Securities Issued by the U.S. Treasury [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		182,634	[3]		358,497	[5]
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		174,464	[6]		136,309	[3]
Recurring Basis [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities	[3]	6,099			6,225
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Fair Value Measurements [Abstract]
Cash equivalents		541,199			221,125
Total		727,708			581,653
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment		0
Recurring Basis [Member] | Quoted Prices in Active Markets (Level 1) [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment		3,875			2,031
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		182,634			358,497
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		1,065,490			1,163,710
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | 0.125% Notes [Member]
Fair Value Measurements [Abstract]
Fair value of convertible notes		495,400
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | 0% Notes [Member]
Fair Value Measurements [Abstract]
Fair value of convertible notes		559,200
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment		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		764,059			846,315
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		120,868			174,861
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		174,464			136,309
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		6,099			6,225
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Abstract]
Cash equivalents		0
Total		14,330			$ 0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Bicycle Therapeutics plc [Member]
Fair Value Measurements [Abstract]
Investment		14,330
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | ProQR Therapeutics N.V. [Member]
Fair Value Measurements [Abstract]
Investment		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		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
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
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
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Municipal Debt Securities [Member]
Fair Value Measurements [Abstract]
Available-for-sale securities		$ 0

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

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

[3] Included in short-term investments.

[4] $10.0 million included in cash and cash equivalents on our consolidated balance sheet, with the difference included in short-term investments on our consolidated balance sheet.

[5] $17.5 million included in cash and cash equivalents on our consolidated balance sheet, with the difference included in short-term investments on our consolidated balance sheet.

[6] $2.3 million included in cash and cash equivalents on our consolidated balance sheet, with the difference included in short-term investments on our consolidated balance sheet.