Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity in the earnings of liability companies or partnerships	$ 5,190	$ 2,533	$ 0
7.75% Subordinated Notes due 2045
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Notes percentage	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%
Subordinated Notes due date	2045