Marketable Securities - Continuous Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Fair Value:
Less than 12 months	$ 14,878
12 months or greater	0
Unrealized Loss:
Less than 12 months	(65)
12 months or greater	0
U.S. treasury debt securities
Fair Value:
Less than 12 months	4,774
12 months or greater	0
Unrealized Loss:
Less than 12 months	(31)
12 months or greater	0
U.S. corporate debt securities
Fair Value:
Less than 12 months	10,104
12 months or greater	0
Unrealized Loss:
Less than 12 months	(34)
12 months or greater	$ 0