Income Taxes (Details 7) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 29, 2012	Dec. 31, 2011	Jan. 01, 2011
Unrecognized Tax Benefits
Unrecognized tax benefits at the beginning of the fiscal year	$ 98,812	$ 131,545	$ 324,837
Gross amount of the increases (decreases) in unrecognized tax benefits of tax positions taken during a prior year	2,194
Gross amount of the increases (decreases) in unrecognized tax benefits of tax positions taken during a prior year		(3,791)	(130,313)
Gross amount of the increases in unrecognized tax benefits as a result of tax positions taken during the current year	3,082	1,588	12,052
Amount of decreases in unrecognized tax benefits relating to settlements with taxing authorities, including the utilization of tax attributes	(11,768)	(30,115)	(74,890)
Reductions to unrecognized tax benefits resulting from the lapse of the applicable statute of limitations	(189)	(421)	(109)
Effect of foreign currency translation	247	6
Effect of foreign currency translation			(32)
Unrecognized tax benefits at the end of the fiscal year	92,378	98,812	131,545
Total amounts of unrecognized tax benefits that, if upon resolution of the uncertain tax positions would reduce Cadence's effective tax rate	57,725	75,057	83,676
Interest and penalties recognized in Income Statements
Interest	(11,184)	2,173	(46,268)
Penalties	(1,862)	(1,495)	4,471
Interest and penalties recognized in Balance Sheets
Interest	24,427	35,368
Penalties	$ 8,953	$ 11,574

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