CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS [Abstract]
Net loss	$ (88,278)	$ (38,984)	$ (60,644)
Unrealized (losses) gains on investments, net of tax	(33,101)	40,079	10,253
Reclassification adjustment for realized (gains) losses included in net loss	(20,211)	(21,412)	(1,653)
Comprehensive loss	$ (141,590)	$ (20,317)	$ (52,044)