Available-for-sale securities (Tables)

6 Months Ended

Jun. 30, 2016

Investments, Debt and Equity Securities [Abstract]

Investments Classified by Contractual Maturity Date [Table Text Block]

The contractual maturities of available-for-sale securities were as follows:

	June 30, 2016
(in thousands)	Less than 12 months		1-3 Years	Over 3 Years	Total
Certificates of deposit	$	—	—	258	258
Corporate bonds	1,004		4,881	1,847	7,732
Total	$	1,004	4,881	2,105	7,990

Available-for-sale Securities [Table Text Block]

	June 30, 2016
(in thousands)	Amortized Cost		Gains in Accumulated Other Comprehensive Loss	Losses in Accumulated Other Comprehensive Loss		Estimated Fair Value
Certificates of deposit	$	250	8	—		258
Corporate bonds	7,746		—	(14	)	7,732
Total	$	7,996	8	(14	)	7,990
(in thousands)	December 31, 2015
	Amortized Cost		Gains in Accumulated Other Comprehensive Loss	Losses in Accumulated Other Comprehensive Loss		Estimated Fair Value
Certificates of deposit	$	1,500	1	—		1,501
Corporate bonds	6,465		—	(44	)	6,421
	$	7,965	1	(44	)	7,922