Estimated title losses - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Current year estimated loss (percent)	3.80%	4.80%	4.80%
Net increase (decrease) in loss reserve estimates for prior policy years	$ 1,034	$ 6,131	$ (1,164)
Reduction in prior policy year reserve	4,000
Change in prior years reserve, large title claims
Gain (Loss) on Securities [Line Items]
Total provisions related to prior policy years	$ 4,400	$ 4,300	$ 3,800