Common Stock and Noncontrolling Interest in Subsidiaries - Additional Information (Details) - USD ($)			1 Months Ended							3 Months Ended
		May 28, 2020	Dec. 31, 2020	Nov. 30, 2020	Aug. 31, 2020	May 31, 2020	Apr. 30, 2020	Feb. 28, 2019	Dec. 31, 2018	Mar. 31, 2021	Mar. 31, 2020
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Common stock, shares authorized			34,900,878							150,000,000
Dividends declared										$ 0
Common stock, voting rights										Each share of common stock entitles the holder to one vote and to receive dividends when and if declared by the board of directors of the Company.
Shares sold/issued			29,381,125							43,516,125
Losses attributed to noncontrolling interests										$ 1,489,000	$ (190,000)
Aggregate purchase price	[1]										14,250,000
MICA
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued			3,367,804
Shares price per share			$ 0.23
Aggregate purchase price			$ 800,000
Ownership interest percentage			35.00%
MICA
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Equity at acquisition		$ 12,800,000
Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional shares issued										13,685,000
Series A Senior Preferred Stock | MICA
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Equity at acquisition		7,100,000
Junior Preferred and Common Stockholders | Noncontrolling Interest in Subsidiaries | MICA
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Equity at acquisition		$ 5,700,000
Cullinan Apollo Corp
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests										$ 0	0
Cullinan Apollo Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued									7,000,000
Gross proceeds									$ 7,000,000
Shares price per share									$ 1.00
Cullinan Apollo Corp | Series A Preferred Stock | Maximum
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued									11,000,000
Cullinan Pearl Corp | Subscription Agreement between Company and Pearl | Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares price per share				$ 0.44
Aggregate purchase price				$ 1,200,000
Purchase of shares				2,730,227
Cullinan Pearl Corp | Taiho Ventures’ Preferred Stock Ownership in Pearl | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests										1,700,000	(200,000)
Cullinan Pearl Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued					9,000,000
Gross proceeds					$ 9,000,000
Cullinan Pearl Corp | Series A Preferred Stock | Taiho Ventures, LLC
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued								14,000,000
Gross proceeds								$ 14,000,000
Shares price per share								$ 1.00
Cullinan Pearl Corp | Series A Preferred Stock | Taiho License Agreement
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued					1,206,000			1,860,000
Aggregate purchase price								$ 0
Additional consideration received					$ 0
Cullinan Pearl Corp | Series A Preferred Stock | Maximum | Taiho Ventures, LLC
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued								23,000,000
Cullinan Amber Corp
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests										0	0
Cullinan Amber Corp | License Agreement between Amber and Massachusetts Institute of Technology
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued							400,132
Cullinan Amber Corp | License Agreement between Amber and Massachusetts Institute of Technology | Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional consideration received							$ 0
Cullinan Amber Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Gross proceeds							$ 3,000,000
Shares issued							3,000,000
Closing price per share							$ 1.00
Cullinan Amber Corp | Series A Preferred Stock | Maximum
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Sale of stock							9,000,000
Cullinan Florentine Corp
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests										0	$ 0
Cullinan Florentine Corp | Tübingen License Agreement
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares sold/issued							725,118
Cullinan Florentine Corp | Tübingen License Agreement | Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional consideration received							$ 0
Additional shares issued			381,810
Cullinan Florentine Corp | Tübingen License Agreement | Common Stock | DFKZ and UFE Anti-dilution Shares
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional consideration received			$ 0
Cullinan Florentine Corp | Series A Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Gross proceeds			$ 6,000,000				$ 6,000,000
Sale of stock							6,000,000
Closing price per share							$ 1.00
Additional shares issued			6,000,000
Cullinan Florentine Corp | Series A Preferred Stock | Maximum
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Sale of stock							6,000,000
MICA | HLBV
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests										$ 200,000
MICA | Series A Senior Preferred Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Shares price per share						$ 1.31
Shares issued						6,088,282
Number of share purchased as part of asset acquisition						5,385,787

[1] Changes in equity activities for the three months ending March 31, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.