Short-term Investments (Details) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	$ 19,403,000
Available-for-sale securities, gross unrealized gains	40,000
Available-for-sale securities, gross unrealized losses	0
Available-for-sale securities, fair value	$ 19,443,000
Investment Maturity Date	Dec. 31, 2017
Available-for-sale Securities, Gross Realized Losses		$ 617,000
Proceeds from Sale and Maturity of Marketable Securities	$ 43,232,000	$ 82,115,000

The maturity date of the investment.

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