Consolidated Statements of Comprehensive Margin - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Consolidated Statements of Comprehensive Margin
Net margin	$ 10,852	$ 17,196	$ 26,221	$ 36,419
Other comprehensive margin:
Unrealized (loss) gain on available-for-sale securities	(314)	431	(361)	827
Total comprehensive margin	$ 10,538	$ 17,627	$ 25,860	$ 37,246