Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Marketable Securities - Schedule of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	$ 11,205	$ 10,186	$ 80,309	$ 21,679
Amortized Cost	227,408	128,212
Gross Unrealized Gains	64	12
Gross Unrealized (Losses)	(11)
Estimated Fair Value	227,461	128,224
Cash equivalents [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	7,193	6,934
Total cash equivalents	7,193	6,934
Available-for-sale securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	220,215
Gross Unrealized Gains	64
Gross Unrealized (Losses)	(11)
Estimated Fair Value	220,268
Money market funds [Member] \| Cash equivalents [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	7,193	6,934
Total cash equivalents	7,193	6,934
Commercial paper securities [Member] \| Available-for-sale securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	36,195
Gross Unrealized Gains	53
Estimated Fair Value	36,248
Corporate debt securities [Member] \| Available-for-sale securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	20,621
Gross Unrealized (Losses)	(11)
Estimated Fair Value	20,610
U.S. government sponsored entity debt securities [Member] \| Available-for-sale securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	163,399	121,278
Gross Unrealized Gains	11	12
Estimated Fair Value	$ 163,410	$ 121,290