Income Taxes (Details 5) - USD ($) $ in Thousands		12 Months Ended
		Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Unrecognized Tax Benefits
Unrecognized tax benefits at the beginning of the fiscal year		$ 110,179	$ 98,540	$ 87,820
Gross amount of the decreases in unrecognized tax benefits of tax positions taken during a prior year	[1]	(4,183)	(688)	(155)
Gross amount of the increases in unrecognized tax benefits as a result of tax positions taken during the current year		2,370	13,141	11,342
Reductions to unrecognized tax benefits resulting from the lapse of the applicable statute of limitations		(5,179)	(3,028)	(149)
Increase resulting from foreign currency translation			838
Decrease resulting from foreign currency translation		(1,330)		(318)
Unrecognized tax benefits at the end of the fiscal year		101,857	110,179	98,540
Total amounts of unrecognized tax benefits that, if upon resolution of the uncertain tax positions would reduce Cadence's effective tax rate		58,022	63,108	56,248
Interest and penalties recognized in Income Statements
Interest		585	1,865	1,166
Penalties		342	218	$ 3
Interest and penalties recognized in Balance Sheets
Interest		2,699	2,511
Penalties		$ 10	$ 151

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