Financial instruments (Tables)

12 Months Ended

Dec. 31, 2017

The Company’s short-term and long-term investments consist of available-for-sale securities as follows:


(in thousands) December 31, 2017	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Short-term investments:
U.S. treasury securities	$	56,123	$	—	$	(70	)	$	56,053

Contractual maturities:
Due within one year	$	56,123						$	56,053
December 31, 2016	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Short-term investments:
U.S. treasury securities	$	70,819	$	—	$	(61	)	$	70,758

Long-term investments:
U.S. treasury securities	$	50,155	$	—	$	(109	)	$	50,046

Contractual maturities:
Due within one year	$	70,819						$	70,758
Due after one year through two years		50,155							50,046

The aggregate estimated fair value of the Company’s investments with unrealized losses are as follows:


	Period of continuous unrealized loss
(in thousands)	12 months or less					Greater than 12 months
	Fair value		Gross unrealized losses			Fair value		Gross unrealized losses
December 31, 2017
U.S. treasury securities	$	15,983	$	(27	)	$	40,070	$	(43	)

December 31, 2016
U.S. treasury securities	$	120,804	$	(170	)		N/A		N/A

The following tables present the fair value of our financial instruments that are measured at fair value on a recurring basis:


(in thousands)	QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1)		OTHER OBSERVABLE INPUTS (LEVEL 2)		SIGNIFICANT UN-OBSERVABLE INPUTS (LEVEL 3)		TOTAL
BALANCES – December 31, 2017
Short-term investments – U.S. treasury securities	$	56,053	$	—	$	—	$	56,053

	$	56,053	$	—	$	—	$	56,053

BALANCES – December 31, 2016
Short-term investments – U.S. treasury securities	$	70,758	$	—	$	—	$	70,758
Long-term investments – U.S. treasury securities		50,046		—		—		50,046

	$	120,804	$	—	$	—	$	120,804