Convertible debt (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Convertible Debt [Table Text Block]

The Notes consist of the following (in thousands):

	September 30, 2018			December 31, 2017
Liability component:
Principal	$	250,000		$	250,000
Less: debt discount and issuance cost, net of amortization	(27,876		)	(36,797		)
Net carrying amount	$	222,124		$	213,203
Equity component(1)	$	37,560		$	37,560

(1) Recorded within additional paid-in capital in the consolidated balance sheet. As of September 30, 2018, it included $28.7 million and $8.8 million related to the 2019 Notes and the 2047 Notes, respectively, net of $1.2 million and $0.3 million issuance cost in equity, respectively.

The following table sets forth total interest expense recognized related to the Notes (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
2.0% coupon	$	1,250	$	1,250	$	3,750	$	2,741
Amortization of debt issuance costs	357		340		1,058		782
Amortization of debt discount	2,659		2,504		7,863		5,555
Total	$	4,266	$	4,094	$	12,671	$	9,078