Marketable Securities - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Fixed Income Securities	$ 1,200,000		$ 1,200,000		$ 5,300,000
Purchases of marketable securities			0	$ 18,876,000
Proceeds from sales of marketable securities			4,073,000	13,901,000
Realized gains on sale of marketable securities	7,000	$ 0	9,000	192,000
Unrealized holding gain arising during the period	$ 2,000	$ 0	$ 5,000	$ 7,000
Marketable securities, effective maturity period (in years)			11 months 27 days
Marketable securities, average effective duration (in years)			1 month 21 days