Equity investees - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Subsidiary, Sale of Stock [Line Items]
Net premium revenues from policies issued by equity investees		$ 28,843,000	$ 31,562,000	$ 42,105,000
Earnings related to equity investees		8,830,000	7,914,000	8,064,000
Goodwill related to equity investees		217,722,000	251,868,000	231,838,000
Impairment of goodwill	$ 35,900,000	35,749,000	0	0
Direct Operations
Subsidiary, Sale of Stock [Line Items]
Net premium revenues from policies issued by equity investees		2,500,000	3,100,000	4,400,000
Earnings related to equity investees		3,600,000	3,400,000	$ 4,100,000
Equity securities
Subsidiary, Sale of Stock [Line Items]
Goodwill related to equity investees		7,400,000	7,400,000
Impairment of goodwill		$ 0	$ 0