Marketable Securities Marketable Securities (Details 1) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	$ 133,697	$ 121,151
Cash, fair value	53,928	51,031
Cash, Cash Equivalents and Short Term Investments, Fair Value Disclosure	187,625	172,182
Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	123,527	84,263
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	$ 10,170	$ 36,888