Short-term Investments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost		$ 58,819
Available-for-sale securities, gross unrealized gains		2
Available-for-sale securities, gross unrealized losses		(263)
Available-for-sale securities, fair value		58,558
Available-for-sale Securities, Gross Realized Gains			$ 1,174
Available-for-sale Securities, Gross Realized Losses	$ 617	2,188	981
Proceeds from Sale and Maturity of Marketable Securities	$ 82,115	$ 182,115	$ 239,370
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Maturity Date	Dec. 31, 2015

The maturity date of the investment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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