Income Taxes Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 28, 2013	Sep. 29, 2012	Sep. 28, 2013	Sep. 29, 2012	Dec. 29, 2012
Unrecognized tax benefits
Unrecognized tax benefits as of December 29, 2012			$ 92,378
Gross amount of the increases in unrecognized tax benefits of tax positions taken during a prior year			6,476
Gross amount of the increases in unrecognized tax benefits as a result of tax positions taken during the current year			13,088
Amount of decreases in unrecognized tax benefits relating to settlements with taxing authorities, including the utilization of tax attributes			(13,821)
Reductions to unrecognized tax benefits resulting from the lapse of the applicable statute of limitations			(12,044)
Effect of foreign currency translation			497
Unrecognized tax benefits as of September 28, 2013	86,574		86,574
Total amounts of unrecognized tax benefits that, if upon resolution of the uncertain tax positions would reduce Cadence's effective tax rate as of September 28, 2013	49,914		49,914
Interest and penalties recognized in the condensed consolidated income statements
Interest	728	820	(12,731)	2,584
Penalties	(708)	(36)	(7,666)	(1,012)
Interest and penalties recognized in the condensed consolidated balance sheets
Interest	52		52		24,427
Penalties	$ 1,255		$ 1,255		$ 8,953