Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) EquityUnit	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Contingencies And Commitments [Line Items]
Number of private equity funds | EquityUnit	2
Commitments towards private equity funds	$ 7.7
Operating leases expiration year	2025
Rental expense	$ 4.2	$ 4.9	$ 4.7
Investment Commitments [Member]
Contingencies And Commitments [Line Items]
Aggregate investment committed in private equity funds	7.9
Private Equity Funds [Member]
Contingencies And Commitments [Line Items]
Contribution to private equity funds	$ 8.4