Summary of Significant Accounting Policies - Available-for-Sale Securities and Trading Securities and Investments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) trust	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Investments
Number of trusts that holds marketable securities | trust	1
Trading securities	$ 10,371	$ 13,172
Net realized and unrealized gain (loss) on trading securities	$ 56	$ 1,112	$ 2,283
Crossroads Systems, Inc.
Investments
Cost method investment (as a percent)	2.00%	4.00%
Cost method investment, carrying value	$ 624	$ 1,457