Summary of Cash, Cash Equivalents, Short-Term investments, and Restricted Cash and Investments - Summary of unrealized gains and losses (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 70,322	$ 70,278
Gross Unrealized Gains	4
Gross Unrealized Losses	(5)	(29)
Fair Value	70,321	70,249
Money market accounts
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	31,957	46,955
Fair Value	31,957	46,955
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11,860	11,318
Fair Value	11,860	11,318
Corporate bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,204	5,694
Gross Unrealized Gains	2
Gross Unrealized Losses	(4)	(18)
Fair Value	8,202	5,676
Government-sponsored enterprise obligations
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,298	3,290
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)	(6)
Fair Value	6,298	3,284
Commercial papers
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,632	1,398
Fair Value	9,632	1,398
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,750	1,000
Gross Unrealized Gains	1
Gross Unrealized Losses		(3)
Fair Value	1,751	997
Sovereign government bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	621	623
Gross Unrealized Losses		(2)
Fair Value	621	621
Cash equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	31,957	46,955
Fair Value	31,957	46,955
Short-term investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	38,365	23,323
Gross Unrealized Gains	4
Gross Unrealized Losses	(5)	(29)
Fair Value	$ 38,364	$ 23,294

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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