Investments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales of marketable securities	$ 9,716,000	$ 141,000	$ 861,000
Realized gain on available-for-sale securities	6,000	0	$ 0
Gross realized gains or losses from sales of marketable securities		$ 0
Gross proceeds associated with realized gains	$ 7,200,000