Net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share Reconciliation [Abstract]
Net loss	$ (8,976)	$ (10,910)	$ (1,109)	$ (2,729)	$ (19,886)	$ (3,838)
Basic:
Shares outstanding at beginning of period (in shares)		18,244,000		16,044,000			16,629,000	16,041,000
Weighted average shares issued during the period, net (in shares)	0		246,000		1,463,000	44,000
Weighted average common shares, basic (in shares)	18,244,000		16,290,000		18,092,000	16,085,000
Net loss per common share, basic (in dollars per shares)	$ (0.49)		$ (0.07)		$ (1.10)	$ (0.24)
Diluted:
Weighted average common shares, basic (in shares)	18,244,000		16,290,000		18,092,000	16,085,000
Weighted average common shares, diluted (in shares)	18,244,000		16,290,000		18,092,000	16,085,000
Net loss per common share, diluted (in dollars per share)	$ (0.49)		$ (0.07)		$ (1.10)	$ (0.24)
Convertible Notes | Convertible Senior Notes due 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price (in dollars per share)	28.55				28.55
Convertible Notes | Convertible Senior Notes Due 2026
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price (in dollars per share)	$ 42.97				$ 42.97
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)					928,000	469,000
Convertible Debt Securities | Convertible Notes | Convertible Senior Notes due 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)					481,548
Convertible Debt Securities | Convertible Notes | Convertible Senior Notes Due 2026
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)					2,792,664