Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net loss	$ (121,122)	$ (95,419)	$ (68,889)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	5,682	3,930	2,359
Amortization of discount on marketable securities	(825)	(4,708)	(5,829)
Amortization and other changes in right-of-use assets	(7,687)	(5,677)	0
Gain on free shares	(63)	(488)	0
Net loss on disposal of property and equipment	222	68	0
Stock-based compensation	25,708	19,330	14,677
Net loss on lease termination	0	218	0
Build-to-suit leases		0	966
Net changes in operating assets and liabilities:
Interest receivable	(353)	(307)	(135)
Accounts receivable	31,685	(32,236)	(1,330)
Prepaid expenses and other assets	(10,411)	(6,660)	(2,828)
Accounts payable and other accrued liabilities	10,703	(4,192)	(6,372)
Accrued compensation and employee benefits	6,877	4,129	2,604
Deferred revenues	216,546	(35,693)	99,364
Long-term portion of lease liabilities	(3,761)	(1,800)	0
Other non-current liabilities	1,300	3,749	1,963
Net cash provided by (used in) operating activities	169,875	(144,402)	36,550
Investing Activities:
Acquisition, net of cash acquired	0	0	(75,647)
Purchases of marketable securities	(570,779)	(443,711)	(451,239)
Maturities of marketable securities	314,570	404,847	391,845
Purchases of property and equipment	(14,714)	(20,675)	(43,065)
Purchase of additional Sangamo France shares	(704)	(262)	0
Net cash used in investing activities	(271,627)	(59,801)	(178,106)
Financing Activities:
Proceeds from public offering of common stock, net of issuance costs	0	136,308	215,758
Proceeds from issuance of common stock in connection with the Biogen collaboration agreement, net of issuance costs	142,526	0	0
Taxes paid related to net share settlement of equity awards	(765)	(422)	(254)
Proceeds from issuance of common stock under employee stock purchase plan	2,015	2,044	1,484
Proceeds from exercise of stock options and restricted stock units	9,324	4,099	14,721
Net cash provided by financing activities	153,100	142,029	231,709
Effect of exchange rate changes on cash and cash equivalents	(447)	184	439
Net increase (decrease) in cash, cash equivalents, and restricted cash	50,901	(61,990)	90,592
Cash, cash equivalents, and restricted cash, beginning of period	81,928	143,918	53,326
Cash, cash equivalents, and restricted cash, end of period	132,829	81,928	143,918
Supplemental cash flow disclosures:
Non-controlling interest for acquisition	0	0	1,313
Right-of-use assets obtained in exchange for lease obligations	1,333	31,291	0
Property and Equipment
Supplemental cash flow disclosures:
Capital expenditures included in unpaid liabilities	4,569	2,114	4,953
Build-to-Suit Leases
Supplemental cash flow disclosures:
Capital expenditures included in unpaid liabilities	$ 0	$ 0	$ 2,950