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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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants to purchase redeemable convertible preferred stock, included in other long term liabilities	$ 0	$ 290	$ 236
(level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants to purchase redeemable convertible preferred stock, included in other long term liabilities	0	0	0
(level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants to purchase redeemable convertible preferred stock, included in other long term liabilities	0	0	0
(level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants to purchase redeemable convertible preferred stock, included in other long term liabilities	0	290	$ 236
US Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	0	3,516
US Treasury obligations \| (level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	0	3,516
US Treasury obligations \| (level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	0	0
US Treasury obligations \| (level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	0	0
Corporate bonds, included in investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	24,785	0
Corporate bonds, included in investments \| (level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	24,785	0
Corporate bonds, included in investments \| (level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	0	0
Corporate bonds, included in investments \| (level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in investments	0	0
Money market funds, included in cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	183
Money market funds, included in cash equivalents \| (level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	183
Money market funds, included in cash equivalents \| (level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	0
Money market funds, included in cash equivalents \| (level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	0
Tri-party repurchase agreements, included in cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	27,000
Tri-party repurchase agreements, included in cash equivalents \| (level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	0
Tri-party repurchase agreements, included in cash equivalents \| (level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	27,000
Tri-party repurchase agreements, included in cash equivalents \| (level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents	$ 0
US Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents		14,486
US Treasury obligations \| (level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents		14,486
US Treasury obligations \| (level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents		0
US Treasury obligations \| (level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in cash equivalents		$ 0