Financial Instruments - Cash And Cash Equivalents And Investments From Continuing Operations (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Cash	$ 211,098	$ 157,317
Money market funds	31,730	122,827
Total cash and cash equivalents	242,828	280,144
Total short-term investments (available-for-sale)	130,507	160,610
Total cash and cash equivalents and short-term investments	373,335	440,754
Cash, Gross Unrealized Gain
Money market funds, Gross Unrealized Gain		448
Total cash and cash equivalents, Gross Unrealized Gain		448
Short-term investments (available-for-sale), Gross Unrealized Gain		31
Total cash and cash equivalents and short-term investments, Gross Unrealized Gain		479
Cash, Gross Unrealized (Loss)
Money market funds, Gross Unrealized (Loss)
Total cash and cash equivalents, Gross Unrealized (Loss)
Short-term investments (available-for-sale), Gross Unrealized (Loss)	(12)	(34)
Total cash and cash equivalents and short-term investments, Gross Unrealized (Loss)	(12)	(34)
Cash, Fair Value	211,098	157,317
Money market funds, Fair Value	31,730	123,275
Total cash and cash equivalents, Fair Value	242,828	280,592	252,673	260,644
Long-term investments (available-for-sale), Fair Value	141,110	171,022
Total short-term investments (available-for-sale), Fair Value	130,495	160,607
Total cash and cash equivalents and short-term investments, Fair Value	373,323	441,199
US Treasury Bill [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Short-term investments (available-for-sale), Cost	103,984	133,648
Short-term investments (available-for-sale), Gross Unrealized Gain		31
Short-term investments (available-for-sale), Gross Unrealized (Loss)	(11)	(5)
Long-term investments (available-for-sale), Fair Value	103,973	133,674
U.S. Government Agencies [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Short-term investments (available-for-sale), Cost	26,523	26,962
Short-term investments (available-for-sale), Gross Unrealized (Loss)	(1)	(29)
Long-term investments (available-for-sale), Fair Value	26,522	26,933
Municipal Bonds [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Long-term investments (available-for-sale), Cost	11,150	11,150
Long-term investments (available-for-sale), Gross Unrealized Gain
Long-term investments (available-for-sale), Gross Unrealized (Loss)	(535)	(735)
Long-term investments (available-for-sale), Fair Value	$ 10,615	$ 10,415