Income Taxes Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012	Dec. 29, 2012
Unrecognized tax benefits
Unrecognized tax benefits as of December 29, 2012			$ 92,378
Gross amount of the increases (decreases) in unrecognized tax benefits of tax positions taken during a prior year			1,025
Gross amount of the increases (decreases) in unrecognized tax benefits as a result of tax positions taken during the current year			13,262
Amount of decreases in unrecognized tax benefits relating to settlements with taxing authorities, including the utilization of tax attributes			(13,635)
Reductions to unrecognized tax benefits resulting from the lapse of the applicable statute of limitations			(12,044)
Effect of foreign currency translation			155
Unrecognized tax benefits as of June 29, 2013	81,141		81,141
Total amounts of unrecognized tax benefits that, if upon resolution of the uncertain tax positions would reduce Cadence's effective tax rate as of June 29, 2013	45,127		45,127
Interest and penalties recognized in the condensed consolidated income statements
Interest	(14)	1,194	(13,459)	1,763
Penalties	1,347	(6)	(6,959)	(975)
Interest and penalties recognized in the condensed consolidated balance sheets
Interest	3,096		3,096		24,427
Penalties	$ 1,964		$ 1,964		$ 8,953