Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity in the earnings of liability companies or partnerships	$ 900	$ 100	$ 3,749	$ 1,448
7.75% Subordinated Notes due 2045
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Notes percentage	7.75%		7.75%
Subordinated Notes due date			2045
Fair Value, Inputs, Level 1 | 7.75% Subordinated Notes due 2045
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Notes percentage	7.75%		7.75%
Subordinated Notes due date			2045