Stock repurchase program (Details) - USD ($) $ / shares in Units, $ in Thousands	10 Months Ended	12 Months Ended	22 Months Ended	180 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2019	Mar. 01, 2018
Stock repurchase program [Abstract]
Authorized value of common stock to be repurchased					$ 5,000
Common stock repurchased (in shares)				4,044,842
Value of common stock repurchased				$ 32,110
Average purchase price of common stock repurchased (in dollars per share)				$ 7.94
2018 Stock Repurchase Program [Member]
Stock repurchase program [Abstract]
Common stock repurchased (in shares)	156,410	0
Value of common stock repurchased	$ 2,000
Average purchase price of common stock repurchased (in dollars per share)	$ 12.79
2016 Stock Repurchase Program [Member]
Stock repurchase program [Abstract]
Common stock repurchased (in shares)			36,465
Value of common stock repurchased			$ 358
Average purchase price of common stock repurchased (in dollars per share)			$ 9.84