Estimated title losses - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Current year estimated loss (percent)	3.80%	3.60%	3.80%
Increase (decrease) in prior year estimates		$ 38.2	$ 16.7
Increase (decrease) in liability claims provision	$ 18.6
Change in prior years reserve, claims payment experience
Gain (Loss) on Investments [Line Items]
Increase (decrease) in liability claims provision	14.3
Recorded provisions		6.2	17.9
Change in prior years reserve, large title claims
Gain (Loss) on Investments [Line Items]
Increase (decrease) in liability claims provision	$ 3.8	$ 31.7	$ 3.1