Stockholders' Equity - Narrative (Details)						1 Months Ended		3 Months Ended		12 Months Ended			14 Months Ended
	Feb. 28, 2021 shares	Feb. 25, 2021 USD ($)	Mar. 12, 2020 USD ($)	Nov. 12, 2019 USD ($)	Dec. 12, 2018 installment shares	May 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Mar. 31, 2021 USD ($) shares	Mar. 31, 2020 USD ($) shares	Dec. 31, 2021 USD ($) installment $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Feb. 24, 2022 USD ($) shares	Feb. 22, 2022 $ / shares	Jun. 05, 2020 shares	Jun. 04, 2020 shares	Dec. 31, 2018 shares	Feb. 28, 2014 shares
Class of Stock [Line Items]
Common stock, authorized (in shares)										350,000,000	350,000,000				350,000,000	175,000,000
Common stock, par value (in dollars per share) | $ / shares										$ 0.00001	$ 0.00001
Common stock, issued (in shares)										177,000,963	148,074,085
Common stock, outstanding (in shares)										177,000,963	148,074,085
Preferred stock, authorized (in shares)										25,000,000	25,000,000
Preferred stock, par value (in dollars per share) | $ / shares										$ 0.00001	$ 0.00001
Preferred stock, issued (in shares)										0	0
Preferred stock, outstanding (in shares)										0	0
Proceeds from the issuance of common stock, net of issuance costs | $										$ 88,202,000	$ 209,419,000	$ 25,785,000
Common stock, shares reserved for future issuance (in shares)										26,423,704	23,566,853
Weighted average grant date fair value (in dollars per share) | $ / shares										$ 2.29	$ 5.63	$ 3.85
Exercise of options (in shares)										0
Intrinsic value of options exercised | $										$ 0	$ 400,000	$ 1,300,000
Fair value of options vested | $										10,600,000	6,800,000	4,300,000
Stock-based compensation expense | $										$ 22,735,000	$ 24,460,000	11,925,000
Subsequent Event
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares														$ 0.00001
Inducement Award Program
Class of Stock [Line Items]
Number of shares granted (in shares)										1,373,200
Number of shares outstanding (in shares)										1,238,200
Stock options
Class of Stock [Line Items]
Number of shares granted (in shares)										3,651,400
Number of shares outstanding (in shares)										11,398,215	9,370,373
Number of shares issued (in shares)	1,997,200
Options expiration after the date of grant										10 years
Stock-based compensation expense | $										$ 8,900,000	$ 8,500,000	5,400,000
Exercise of options (in shares)										0
Intrinsic value of options exercised | $										$ 0
Stock-based compensation expense | $										$ 8,958,000	8,517,000	5,421,000
Stock options | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage										100.00%
Stock options | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting periods										1 year
Vesting percentage										25.00%
Stock options | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Vesting periods										1 year
Number of equal quarterly installments | installment										12
Restricted stock units
Class of Stock [Line Items]
Number of shares granted (in shares)	3,180,400
Stock-based compensation expense | $										$ 12,927,000	14,639,000	6,240,000
Restricted stock units | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting periods										1 year
Restricted stock units | Share Based Compensation Award Tranche One | Keryx Biopharmaceuticals, Inc.
Class of Stock [Line Items]
Vesting periods					1 year
Restricted stock units | Share Based Compensation Award Tranche Two | Keryx Biopharmaceuticals, Inc.
Class of Stock [Line Items]
Vesting periods					1 year
Vesting percentage					33.33%
Restricted stock units | Share-based Payment Arrangement, Tranche Three | Keryx Biopharmaceuticals, Inc.
Class of Stock [Line Items]
Award vesting quarterly period					2 years
Restricted stock units | Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting periods										1 year
Vesting percentage										33.33%
Restricted stock units | Share-Based Payment Arrangement, Tranche Two, Second Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting periods										2 years
Vesting percentage										33.33%
Restricted stock units | Share-Based Payment Arrangement, Tranche Three, Third Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting periods										3 years
Vesting percentage										33.33%
Performance Based Restricted Stock Unit
Class of Stock [Line Items]
Number of shares granted (in shares)										37,150
Stock-based compensation expense | $										$ 294,000	$ 464,000	0
Performance-Based Stock Options
Class of Stock [Line Items]
Number of shares granted (in shares)										99,558	0
Weighted average grant date fair value (in dollars per share) | $ / shares										$ 2.74
Number of shares outstanding (in shares)										99,558	0
Stock-based compensation expense | $										$ 0	$ 0	$ 0
Vested in period (in shares)										0	0	46,790
Service Based Restricted Stock Units | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage										50.00%
Service Based Restricted Stock Units | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Vesting periods										6 months
Vesting percentage										25.00%
Award vesting grace period										1 year
Service Based Restricted Stock Units | Share-based Compensation Award, Tranche, First Or Third Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage										100.00%
Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)
Class of Stock [Line Items]
Number of shares granted (in shares)										3,518,762
Weighted average grant date fair value (in dollars per share) | $ / shares										$ 3.44
Weighted average period of recognition for unrecognized compensation costs										1 year 6 months 21 days
Number of shares outstanding (in shares)										4,554,343	4,725,353
Vested in period | $										$ 15,400,000	$ 9,400,000	$ 2,700,000
Unrecognized compensation cost | $										$ 12,400,000
Merger Agreement | Performance-Based Stock Options
Class of Stock [Line Items]
Converted outstanding RSUs (in shares)										13,102
Keryx Biopharmaceuticals, Inc. | Restricted stock units
Class of Stock [Line Items]
Stock issued related to merger (in shares)					486,709
Number of vesting installments | installment					3
Number of shares outstanding										0
Public Offering
Class of Stock [Line Items]
Sale of stock (in dollars per share) | $ / shares						$ 12.00
Sale of stock, issued in transaction (in shares)						12,650,000
Sale of stock, consideration received | $						$ 142,400,000
Over-Allotment Option
Class of Stock [Line Items]
Sale of stock, issued in transaction (in shares)						1,650,000
Maximum | Stock options
Class of Stock [Line Items]
Vesting periods										48 months
Maximum | Service Based Restricted Stock Units | Share-based Compensation Award, Tranche, First Or Third Anniversary of Grant Date
Class of Stock [Line Items]
Vesting periods										3 years
Maximum | At The Market Equity Offering Program Authorized February 2021
Class of Stock [Line Items]
Common stock sales agreement amount | $		$ 100,000,000
Minimum | Stock options
Class of Stock [Line Items]
Vesting periods										12 months
Minimum | Service Based Restricted Stock Units | Share-based Compensation Award, Tranche, First Or Third Anniversary of Grant Date
Class of Stock [Line Items]
Vesting periods										1 year
At The Market Equity Offering Program | Maximum
Class of Stock [Line Items]
Common stock sales agreement amount | $			$ 65,000,000	$ 75,000,000
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)																		1,785,000
Incremental rate at which the shares reserved for issuance increase										3.00%
2014 Plans | Inducement Award Program
Class of Stock [Line Items]
Compensation not yet recognized, stock options | $										$ 15,700,000
Weighted average period of recognition for unrecognized compensation costs										2 years 3 months 29 days
2014 Plans | Performance-Based Stock Options
Class of Stock [Line Items]
Compensation not yet recognized, stock options | $										$ 0
2014 Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance (in shares)										5,173,141
Offering period										6 months
Purchase price at the end of offering period										85.00%
Number of shares issued (in shares)										307,193
Stock-based compensation expense | $										$ 556,000	840,000	264,000
Employees | Inducement Award Program
Class of Stock [Line Items]
Number of shares granted (in shares)										1,373,200
Employees | Restricted stock units
Class of Stock [Line Items]
Stock-based compensation expense | $										$ 12,900,000	$ 14,600,000	$ 6,200,000
Employees | 2014 Plans | Stock options
Class of Stock [Line Items]
Number of shares granted (in shares)										1,997,200
Employees | 2014 Plans | Restricted stock units
Class of Stock [Line Items]
Number of shares granted (in shares)										3,399,412
Employees | 2014 Plans | Performance Based Restricted Stock Unit
Class of Stock [Line Items]
Number of shares granted (in shares)										136,708
Director | 2014 Plans | Stock options
Class of Stock [Line Items]
Number of shares granted (in shares)										281,000
Director | 2014 Plans | Restricted stock units
Class of Stock [Line Items]
Number of shares granted (in shares)										82,200
Common Stock
Class of Stock [Line Items]
Common stock, outstanding (in shares)							121,674,568			177,000,963	148,074,085	121,674,568					116,887,518
Issuance of common stock, net of issuance costs (in shares)										26,352,343	24,133,348	4,068,912
Exercise of options (in shares)											166,633	362,796
Common Stock | At The Market Equity Offering Program Authorized February 2021 | Subsequent Event
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs (in shares)													21,532,665
Proceeds from the issuance of common stock, net of issuance costs | $													$ 73,200,000
Common Stock | At The Market Equity Offering Program
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs (in shares)							2,684,392	5,224,278	7,973,967		3,509,381
Proceeds from the issuance of common stock, net of issuance costs | $							$ 16,800,000	$ 15,900,000	$ 56,700,000		$ 10,600,000