Cash, Cash Equivalents, and Investments - Components of Cash, Cash Equivalents and Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Apr. 01, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 32,290	$ 34,986
Cash equivalents	9,398	5,098
Money market instruments	1,069	5,076
Cash and cash equivalents	42,757	45,160	41,559	38,103
Short-term investments	125,411	105,105
Limited partnership interest (accounted for using cost method)	3,740	3,740
Long-term investments	245,484	238,255
Total	413,652	388,520
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	60,962	46,001
Long-term investments	110,443	100,072
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	22,982	17,666
Long-term investments	42,337	34,710
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	12,952	16,224
Long-term investments	16,619	17,846
Agency bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	11,493	7,482
Long-term investments	27,785	29,441
Treasury bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	5,604	5,997
Long-term investments	28,123	36,276
Covered bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	4,660	5,618
Long-term investments	6,611	5,564
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	2,998
Sovereign bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	1,997	3,986
Long-term investments	9,826	10,606
Corporate stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	$ 1,763	$ 2,131