Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 24,043	$ 17,483	$ 33,707
Gross Unrealized Gains	11	1	2
Gross Unrealized Losses		(2)	(5)
Fair Value	24,054	17,482	33,704
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,527	2,768	8,369
Marketable securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	18,322	14,509	24,852
Restricted cash
Schedule of Available-for-sale Securities [Line Items]
Fair Value	205	205	483
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,733	2,973	7,529
Fair Value	5,733	2,973	7,529
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,241		6,748
Gross Unrealized Gains	7		1
Fair Value	4,248		6,749
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,263	6,024	7,478
Gross Unrealized Gains	1
Gross Unrealized Losses		(2)	(3)
Fair Value	5,264	6,022	7,475
U.S. government-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,304	5,435	10,678
Gross Unrealized Gains	3	1	1
Gross Unrealized Losses			(2)
Fair Value	8,307	5,436	10,677
U.S. treasury notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	502	3,051	1,274
Fair Value	$ 502	$ 3,051	$ 1,274

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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