Fair Value of Financial Instruments - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Fair Value [Line Items]
Amortized Cost	$ 477,425	$ 378,952
Unrealized Gains	1,406	903
Unrealized Losses	(122)	(397)
Fair Value	478,709	379,458
Cash excluded	218,100	195,900
Cash Equivalents
Fair Value [Line Items]
Amortized Cost	32,157	36,326
Unrealized Gains	3	4
Unrealized Losses	0	0
Fair Value	32,160	36,330
Short-term marketable securities:
Fair Value [Line Items]
Amortized Cost	195,180	148,952
Unrealized Gains	511	317
Unrealized Losses	(10)	(28)
Fair Value	195,681	149,241
Long-term marketable securities:
Fair Value [Line Items]
Amortized Cost	250,088	193,674
Unrealized Gains	892	582
Unrealized Losses	(112)	(369)
Fair Value	250,868	193,887
Commercial paper \| Short-term marketable securities:
Fair Value [Line Items]
Amortized Cost		4,459
Unrealized Gains		3
Unrealized Losses		(2)
Fair Value		4,460
Corporate bonds \| Short-term marketable securities:
Fair Value [Line Items]
Amortized Cost	59,531	47,155
Unrealized Gains	273	107
Unrealized Losses	0	(3)
Fair Value	59,804	47,259
Corporate bonds \| Long-term marketable securities:
Fair Value [Line Items]
Amortized Cost	86,826	84,414
Unrealized Gains	483	310
Unrealized Losses	(12)	(171)
Fair Value	87,297	84,553
Asset-backed securities \| Long-term marketable securities:
Fair Value [Line Items]
Amortized Cost	1,227	7,426
Unrealized Gains	13	94
Unrealized Losses	0	0
Fair Value	1,240	7,520
U.S. Treasury and government agencies \| Short-term marketable securities:
Fair Value [Line Items]
Amortized Cost	135,649	97,338
Unrealized Gains	238	207
Unrealized Losses	(10)	(23)
Fair Value	135,877	97,522
U.S. Treasury and government agencies \| Long-term marketable securities:
Fair Value [Line Items]
Amortized Cost	162,035	101,834
Unrealized Gains	396	178
Unrealized Losses	(100)	(198)
Fair Value	162,331	101,814
Money market funds \| Cash Equivalents
Fair Value [Line Items]
Amortized Cost	205	404
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	205	404
Commercial paper \| Cash Equivalents
Fair Value [Line Items]
Amortized Cost		1,983
Unrealized Gains		0
Unrealized Losses		0
Fair Value		1,983
U.S. Treasury and government agencies \| Cash Equivalents
Fair Value [Line Items]
Amortized Cost	31,952	33,939
Unrealized Gains	3	4
Unrealized Losses	0	0
Fair Value	$ 31,955	$ 33,943

QUALYS, INC. 10-K