Investments - Other Investments - Additional Information (Detail) $ in Millions	Dec. 31, 2015 USD ($) Investment Venture	Dec. 31, 2014 USD ($)	Sep. 01, 2013
Schedule of Equity Method Investments [Line Items]
Assets	$ 83.6	$ 82.0
Ownership interest held	50.00%		99.00%
Non controlling interest certified low-income housing developments | Investment	12
Non controlling interest in real estate entities | Investment	2
Carrying value of investments in real estate entities	$ 0.0
Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Assets	2.6	$ 3.2
Other Investments [Member] | Four Venture Capital Funds [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 2.1
Non controlling interest in venture capital funds number | Venture	4
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 60.0
Debt	20.0
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Twelve Certified Low-Income Housing Developments [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of investments	$ 0.0
Investment Management Company [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest held	20.00%
Cost of acquiring equity interest	$ 0.5