Cash Equivalents and Investments - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) security
Unrealized loss position
Unrealized loss position for less than 12 months	$ 179,900
Unrealized loss position for more than 12 months	$ 0
Number of held securities in an unrealized loss position | security	33
Realized gain (loss) on sales of investments
Realized gain (loss) on sales of investments	$ 0
Adjustment for other than temporary fair value decline
Adjustment for other than temporary fair value decline	$ 0