Income Taxes (Details 6) - USD ($) $ in Thousands		12 Months Ended
		Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Unrecognized Tax Benefits
Unrecognized tax benefits at the beginning of the fiscal year		$ 98,540	$ 87,820	$ 97,224
Gross amount of the decreases in unrecognized tax benefits of tax positions taken during a prior year	[1]		(155)	(7,331)
Gross amount of the increases in unrecognized tax benefits as a result of tax positions taken during the current year	[1]	688
Gross amount of the increases in unrecognized tax benefits as a result of tax positions taken during the current year		13,141	11,342	7,513
Amount of decreases in unrecognized tax benefits relating to settlements with taxing authorities, including the utilization of tax attributes		0	0	(9,571)
Reductions to unrecognized tax benefits resulting from the lapse of the applicable statute of limitations		(3,028)	(149)	(119)
Increase resulting from foreign currency translation		(838)		(104)
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation			(318)
Unrecognized tax benefits at the end of the fiscal year		110,179	98,540	87,820
Total amounts of unrecognized tax benefits that, if upon resolution of the uncertain tax positions would reduce Cadence's effective tax rate		63,108	56,248	48,335
Interest and penalties recognized in Income Statements
Interest		1,865	1,166	110
Penalties		218	3	$ (127)
Interest and penalties recognized in Balance Sheets
Interest		2,511	1,332
Penalties		$ 151	$ 265

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