Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (91,248)	$ (69,770)	$ (52,642)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net of income tax expense of $9.7 million, $2.2 million, and $0 for the years ended December 31, 2017, 2016, and 2015, respectively (see Note 3(h))	16,039	4,185	(1,429)
Foreign currency translation adjustments	1,539	(445)	(3,040)
Other comprehensive income (loss)	17,578	3,740	(4,469)
Total comprehensive loss	$ (73,670)	$ (66,030)	$ (57,111)