Borrowings (Tables)

6 Months Ended

Jun. 30, 2017

Borrowings consist of the following (in thousands):


	June 30, 2017			December 31, 2016
Facility Financing Obligation (2019 Notes)
Principal amount	$	60,000		$	75,000
Unamortized debt discount		(2,516	)		(3,661	)

Net carrying amount	$	57,484		$	71,339

Senior Convertible Notes (2018 Notes)
Principal amount	$	27,690		$	27,690
Unamortized premium		306			426
Unaccreted debt issuance costs		(347	)		(481	)

Net carrying amount	$	27,649		$	27,635

Note payable to principal stockholder—net carrying amount	$	79,666		$	49,521

Accretion of Debt Issuance Cost and Debt Discount

Accretion of debt issuance cost and debt discount in connection with the Facility Agreement during the three and six months ended June 30, 2017 and 2016, which includes the acceleration of the debt discount and issuance costs related to the transactions disclosed above, are as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Accretion expense—debt issuance cost	$	24	$	9	$	32	$	17

Accretion expense—debt discount	$	686	$	433	$	1,133	$	852

Schedule of Amortization of Premium and Accretion of Debt Issuance Costs

Amortization of the premium and accretion of debt issuance costs related to the 2018 notes for the three and six months ended June 30, 2017 and 2016 are as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Amortization of debt premium	$	61	$	58	$	120	$	115

Accretion expense—debt issuance cost	$	68	$	63	$	134	$	126