Net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 15, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share Reconciliation [Abstract]
Net loss	$ (5,902)	$ (1,109)	$ (2,729)	$ (16,704)	$ (1,323)	$ 68	$ (9,740)	$ (17,959)
Basic:
Shares outstanding at beginning of period (in shares)		16,290,000			15,993,000					16,085,000	15,949,000
Weighted average shares issued/(repurchased) during the period, net (in shares)	10,000			78,000			1,000	84,000
Weighted average common shares, basic (in shares)	16,300,000			16,071,000			16,086,000	16,033,000
Net loss per common share, basic (in dollars per shares)	$ (0.36)			$ (1.04)			$ (0.61)	$ (1.12)
Diluted:
Weighted average common shares, basic (in shares)	16,300,000			16,071,000			16,086,000	16,033,000
Dilutive impact of stock options and restricted stock awards (in shares)	0			0			0	0
Weighted average common shares, diluted (in shares)	16,300,000			16,071,000			16,086,000	16,033,000
Net loss per common share, diluted (in dollars per share)	$ (0.36)			$ (1.04)			$ (0.61)	$ (1.12)
Convertible Notes | Convertible Senior Notes due 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price									$ 28.55
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)							590,000	0
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)							2,801,736