Cash, Cash Equivalents, and Available for Sale Marketable Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Amortized Cost Basis [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 63,507	$ 31,309	$ 66,533	$ 7,035
Total marketable securities, amortized cost	128,862	193,287
Total money market funds and marketable securities	191,870	222,888
Fair Value Disclosure [Abstract]
Cash and cash equivalents, fair value	63,507	31,309	$ 66,533	$ 7,035
Marketable securities, fair value	130,062	193,036
Total money market funds and marketable securities	193,070	222,637
Amortized Cost Abstract
Unrealized gains	1,203
Total money market funds and marketable securities	1,203
Unrealized losses	3	251
Total money market funds and marketable securities	3	251
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Rolling Maturity [Abstract]
Due in one year or less	127,646
Money market funds
Amortized Cost Basis [Abstract]
Cash and Cash Equivalents, at Carrying Value	63,008	29,601
Fair Value Disclosure [Abstract]
Cash and cash equivalents, fair value	63,008	29,601
Debt Securities [Member]
Amortized Cost Basis [Abstract]
Marketable debt securities, amortized cost	127,642
Fair Value Disclosure [Abstract]
Marketable debt securities, fair value	127,646
Amortized Cost Abstract
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	7
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	3
U.S. Treasury notes
Amortized Cost Basis [Abstract]
Marketable debt securities, amortized cost	112,489	158,166
Fair Value Disclosure [Abstract]
Marketable debt securities, fair value	112,486	157,981
Amortized Cost Abstract
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	3	185
U. S. Government agency bonds
Amortized Cost Basis [Abstract]
Marketable debt securities, amortized cost	15,153	35,121
Fair Value Disclosure [Abstract]
Marketable debt securities, fair value	15,160	35,055
Amortized Cost Abstract
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	7
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		$ 66
Equity securities
Amortized Cost Basis [Abstract]
Marketable equity securities, amortized cost	1,220
Fair Value Disclosure [Abstract]
Marketable equity securities, fair value	2,416
Amortized Cost Abstract
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	$ 1,196