Cash Equivalents and Investments - Company's Cash Equivalents and Investments Measured at Fair Value (Detail) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	$ 371,075
Investments measured at fair value	204,457		155,644
Money-market funds [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	364,596		674,219
Government and agencies securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	6,479
Investments measured at fair value	66,700		35,975
Agency securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	129,463		97,408
Non-agency securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	1,393		9,989
Corporate debt securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	6,001		12,272
Commercial paper [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	900
Long-term marketable equity securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	1,689		1,514
Level 1 [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	364,596
Investments measured at fair value	17,042		5,403
Level 1 [Member] | Money-market funds [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	364,596	[1]	674,219	[1]
Level 1 [Member] | Government and agencies securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	17,042	[1]	5,403	[1]
Level 1 [Member] | Long-term marketable equity securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	1,689	[2]	1,514	[2]
Level 2 [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	6,479
Investments measured at fair value	187,415		150,241
Level 2 [Member] | Government and agencies securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Cash equivalents measured at fair value	6,479	[3]
Investments measured at fair value	49,658	[3]	30,572	[3]
Level 2 [Member] | Agency securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	129,463	[3]	97,408	[3]
Level 2 [Member] | Non-agency securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	1,393	[3]	9,989	[3]
Level 2 [Member] | Corporate debt securities [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	6,001	[3]	12,272	[3]
Level 2 [Member] | Commercial paper [Member]
Company's Cash Equivalents and Investments measured at Fair Value [Line Items]
Investments measured at fair value	$ 900	[3]

[1] The fair value of money-market funds is determined using unadjusted prices in active markets. The fair value of Level 1 U.S. government and agency securities is determined using quoted prices in active markets.

[2] The fair value of marketable equity securities is determined using quoted prices in active markets. These amounts are included within other assets in the consolidated balance sheets.

[3] These investments are traded less frequently than Level 1 securities and are valued using inputs that include quoted prices for similar assets in active markets and inputs other than quoted prices that are observable for the asset, such as interest rates, yield curves, prepayment speeds, collateral performance, broker/dealer quotes and indices that are observable at commonly quoted intervals.