Cash Equivalents and Investments - Company's Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Long-term investments in equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale equity securities, Amortized Cost	$ 669	$ 669
Available-for-sale Equity Securities, Gross Unrealized Gain	1,321	1,020
Available-for-sale Equity Securities, Gross Unrealized Loss
Available-for-sale Securities, Equity Securities	1,990	1,689
Asset-backed and mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost	142,541	125,563
Available-for-sale Debt Securities Gross Unrealized Gain	4,862	6,390
Available-for-sale Debt Securities, Gross Unrealized Loss	(2,338)	(1,097)
Available-for-sale Securities, Debt Securities	145,065	130,856
Government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost	84,738	65,904
Available-for-sale Debt Securities Gross Unrealized Gain	447	802
Available-for-sale Debt Securities, Gross Unrealized Loss	(544)	(6)
Available-for-sale Securities, Debt Securities	84,641	66,700
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost	20,848	5,864
Available-for-sale Debt Securities Gross Unrealized Gain	87	137
Available-for-sale Debt Securities, Gross Unrealized Loss	(78)
Available-for-sale Securities, Debt Securities	20,857	6,001
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost	13,345	900
Available-for-sale Debt Securities Gross Unrealized Gain
Available-for-sale Debt Securities, Gross Unrealized Loss
Available-for-sale Securities, Debt Securities	13,345	900
Total short-term debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost	261,472	198,231
Available-for-sale Debt Securities Gross Unrealized Gain	5,396	7,329
Available-for-sale Debt Securities, Gross Unrealized Loss	(2,960)	(1,103)
Available-for-sale Securities, Debt Securities	$ 263,908	$ 204,457