Investments - Short-Term and Long-Term Investments in Debt Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Short-term investments	$ 206,085	$ 185,783
Long-term investments	41,158	59,197
Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	206,078	185,812
Unrealized Gains	47	26
Unrealized Losses	(40)	(55)
Short-term investments	206,085	185,783
Short-term Investments \| U.S. Government Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	32,183	26,930
Unrealized Gains	18	7
Unrealized Losses		(2)
Short-term investments	32,201	26,935
Short-term Investments \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	66,737	59,336
Unrealized Gains	12	7
Unrealized Losses	(5)	(6)
Short-term investments	66,744	59,337
Short-term Investments \| Non-U.S. Government Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	9,556	8,764
Unrealized Gains		2
Unrealized Losses	(1)
Short-term investments	9,555	8,766
Short-term Investments \| Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	97,602	90,782
Unrealized Gains	17	10
Unrealized Losses	(34)	(47)
Short-term investments	97,585	90,745
Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	41,124	59,229
Unrealized Gains	45	7
Unrealized Losses	(11)	(39)
Long-term investments	41,158	59,197
Long-term investments \| U.S. Government Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	15,140	25,320
Unrealized Gains	23	4
Unrealized Losses		(10)
Long-term investments	15,163	25,314
Long-term investments \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	14,040	17,369
Unrealized Gains	13	1
Unrealized Losses		(14)
Long-term investments	14,053	17,356
Long-term investments \| Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	11,944	16,540
Unrealized Gains	9	2
Unrealized Losses	(11)	(15)
Long-term investments	$ 11,942	$ 16,527

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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This item represents the cost of debt 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of investments in debt securities classified as available-for-sale, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature more than one year from the balance sheet date or operating cycle, if longer.

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