Income Taxes (Details 5) - USD ($) $ in Thousands		12 Months Ended
		Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Unrecognized Tax Benefits
Unrecognized tax benefits at the beginning of the fiscal year		$ 101,857	$ 110,179	$ 98,540
Gross amount of the decreases in unrecognized tax benefits of tax positions taken during a prior year	[1]	(3,143)	(4,183)
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	[1]			688
Gross amount of the increases in unrecognized tax benefits as a result of tax positions taken during the current year		8,951	2,370	13,141
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities		(380)	0	0
Reductions to unrecognized tax benefits resulting from the lapse of the applicable statute of limitations		(1,692)	(5,179)	(3,028)
Unrecognized Tax Benefits, Increase Resulting from Foreign Currency Translation		448		838
Decrease resulting from foreign currency translation			(1,330)
Unrecognized tax benefits at the end of the fiscal year		106,041	101,857	110,179
Total amounts of unrecognized tax benefits that, if upon resolution of the uncertain tax positions would reduce Cadence's effective tax rate		61,527	58,022	63,108
Interest and penalties recognized in Income Statements
Interest		490	585	1,865
Penalties		19	342	$ 218
Interest and penalties recognized in Balance Sheets
Interest		3,500	2,699
Penalties		$ 12	$ 10

[1] Includes unrecognized tax benefits of tax positions recorded in connection with acquisitions