Fair Value Measurements (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Assets:
Available for sale securities	$ 518,502,000	$ 723,449,000
Corporate debt securities [Member]
Assets:
Available for sale securities	207,137,000	228,953,000
U.S. government agencies [Member]
Assets:
Available for sale securities	77,364,000	72,840,000
Fair Value, Measurements, Recurring [Member]
Assets:
Money market funds	107,708,000	273,546,000
Derivative assets		623,000
Total	392,209,000	575,962,000
Liabilities:
Derivative liabilities	748,000	549,000
Stock warrant liability		410,000
Total liabilities	2,637,000	959,000
Fair Value, Measurements, Recurring [Member] \| Corporate debt securities [Member]
Assets:
Available for sale securities	207,137,000	228,953,000
Fair Value, Measurements, Recurring [Member] \| U.S. government agencies [Member]
Assets:
Available for sale securities	77,364,000	72,840,000
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets:
Money market funds	107,708,000	273,546,000
Derivative assets		0
Total	107,708,000	273,546,000
Liabilities:
Derivative liabilities	0	0
Stock warrant liability		0
Total liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Corporate debt securities [Member]
Assets:
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| U.S. government agencies [Member]
Assets:
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets:
Money market funds	0	0
Derivative assets		623,000
Total	284,501,000	302,416,000
Liabilities:
Derivative liabilities	748,000	549,000
Stock warrant liability		0
Total liabilities	748,000	549,000
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Corporate debt securities [Member]
Assets:
Available for sale securities	207,137,000	228,953,000
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| U.S. government agencies [Member]
Assets:
Available for sale securities	77,364,000	72,840,000
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets:
Money market funds	0	0
Derivative assets		0
Total	0	0
Liabilities:
Derivative liabilities	0	0
Stock warrant liability		410,000
Total liabilities	1,889,000	410,000
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Corporate debt securities [Member]
Assets:
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| U.S. government agencies [Member]
Assets:
Available for sale securities	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (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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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of shares that an entity is required to redeem for cash or other assets at a fixed or determinable date or upon the occurrence of an event.

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