Financial instruments (Tables)

3 Months Ended

Mar. 31, 2018

Investments, All Other Investments [Abstract]

Summary of Short-Term Investments of Available-for-Sale Securities

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

(in thousands) March 31, 2018	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Short-term investments:
U.S. treasury securities	$	26,074	$	—	$	(24	)	$	26,050
Contractual maturities:
Due within one year	$	26,074						$	26,050
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

Aggregate Estimated Fair Value of Investments with Unrealized Losses

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

(in thousands)	Period of continuous unrealized loss
	12 months or less					Greater than 12 months
March 31, 2018	Fair value		Gross unrealized losses			Fair value		Gross unrealized losses
U.S. treasury securities	$	5,999	$	(9	)	$	20,051	$	(15	)
December 31, 2017
U.S. treasury securities	$	15,983	$	(27	)	$	40,070	$	(43	)

Fair Value of Financial Instruments Measured At Fair Value on a Recurring Basis

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

	QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1)		OTHER OBSERVABLE INPUTS (LEVEL 2)		SIGNIFICANT UN- OBSERVABLE INPUTS (LEVEL 3)		TOTAL
BALANCES – March 31, 2018
Short-term investments – U.S. treasury securities	$	26,050	$	—	$	—	$	26,050
	$	26,050	$	—	$	—	$	26,050
BALANCES – December 31, 2017
Short-term investments – U.S. treasury securities	$	56,053	$	—	$	—	$	56,053
	$	56,053	$	—	$	—	$	56,053