Marketable Securities - Schedule of Investments with Continuous Unrealized Losses (Details) $ in Thousands	Sep. 30, 2017 USD ($) Number	Dec. 31, 2016 USD ($) Number
Total number in loss position | Number	1	1
Less Than 12 Months, Fair Values	$ 402	$ 1,853
Less Than 12 Months, Unrealized Losses	(1)	(13)
12 Months or Greater, Fair Values
12 Months or Greater, Unrealized Losses
Total Fair Values	402	1,853
Total Unrealized Losses	$ (1)	$ (13)
Mutual Funds [Member]
Total number in loss position | Number	1	1
Less Than 12 Months, Fair Values	$ 402	$ 1,853
Less Than 12 Months, Unrealized Losses	(1)	(13)
12 Months or Greater, Fair Values
12 Months or Greater, Unrealized Losses
Total Fair Values	402	1,853
Total Unrealized Losses	$ (1)	$ (13)