Marketable Securities - Scheduled Maturities of Available-for-Sale Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Due within one year, amortized cost	$ 103	$ 0
Due after one year through five years, amortized cost	1,632	1,748
Total, amortized cost	1,735	1,748
Due within one year, fair value	103	0
Due after one year through five years, fair value	1,631	1,728
Total, fair value	$ 1,734	$ 1,728