Net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Feb. 10, 2020	Dec. 31, 2019	Apr. 15, 2019	Dec. 31, 2018
Earnings Per Share Reconciliation [Abstract]
Net loss	$ (10,910)	$ (2,729)
Basic:
Shares outstanding at beginning of period (in shares)				16,629,000		16,041,000
Weighted average shares issued/(repurchased) during the period, net (in shares)	1,312,000	3,000
Weighted average common shares, basic (in shares)	17,941,000	16,044,000
Net loss per common share, basic (in dollars per shares)	$ (0.61)	$ (0.17)
Diluted:
Weighted average common shares, basic (in shares)	17,941,000	16,044,000
Weighted average common shares, diluted (in shares)	17,941,000	16,044,000
Net loss per common share, diluted (in dollars per share)	$ (0.61)	$ (0.17)
Convertible Notes | Convertible Senior Notes due 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price					$ 28.55
Convertible Notes | Convertible Senior Notes Due 2026
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price			$ 42.97
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)	951,000	486,000
Stock options | 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
Stock options | 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