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Investments (Tables)

12 Months Ended

Dec. 31, 2016

Investments

Summary of fair value and unrealized gains (losses) position of available for sale securities

									Gross					Gross
				Amortized					Unrealized					Unrealized					Estimated
				Cost					Gains					Losses					Fair Value
				(in thousands)
December 31, 2016
U.S. treasuries				$	40,013				$	—				$	(5	)			$	40,008
Government agency securities				10,020					—					(8		)			10,012
Corporate debt				13,780					—					(7		)			13,773
Commercial paper				2,994					—					—					2,994

Total				$	66,807				$	—				$	(20	)			$	66,787


December 31, 2015
U.S. treasuries				$	94,935				$	6				$	(23	)			$	94,918
Government agency securities				12,985					3					—					12,988
Corporate debt				8,144					1					(1		)			8,144

Total				$	116,064				$	10				$	(24	)			$	116,050

Summary of fair value and unrealized losses of available-for-sale securities in a loss position

				December 31, 2016										December 31, 2015
									Gross										Gross
				Estimated					Unrealized					Estimated					Unrealized
				Fair Value					Losses					Fair Value					Losses
				(in thousands)
U.S. treasuries				$	20,002				$	(5	)			$	64,922				$	(23	)
Government agency securities				10,012					(8		)			—					—
Corporate debt				13,774					(7		)			3,353					(1		)

Total				$	43,788				$	(20	)			$	68,275				$	(24	)