Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Environmental activities expenditures	$ 2.0	$ 1.2	$ 2.3
Standby letters of credit	16.7
Outstanding commitments to fund new loan and lease transactions	$ 634.7
Funding commitments for loans and leases expiration period	90 days
Other commitments due in 2016	$ 219.9
Other commitments due in 2017	61.1
Other commitments due in 2018	$ 4.0
Other commitments due in 2019
Other commitments due in 2020