Commitments and Contingencies - Additional Information (Detail)		6 Months Ended
	Apr. 05, 2016 USD ($)	Jun. 30, 2016 USD ($) Terms	Dec. 31, 2015 USD ($)
Commitments And Contingencies [Line Items]
Settlement costs	$ 4,750,000
Number of additional successive terms extendable at the option | Terms		4
Period of extendable lease term, in years		5 years
Lease term, description		Less than one year
Sale leaseback transaction, gain recognized over lease term		$ 35,800,000	$ 40,700,000
Loan commitments		2,251,000,000	1,746,000,000
Fixed rate loan commitment		2,136,000,000
Floating rate loan commitment		115,800,000
Standby letters of credit		$ 61,600,000	62,600,000
Loan commitments floating rate, minimum		0.00%
Loan commitments floating rate, maximum		25.00%
Allowance for unfunded loan commitments		$ 4,400,000	3,600,000
Extended credit		13,800,000	14,500,000
Credit extensions with collateral		$ 12,900,000	$ 13,600,000
Minimum [Member]
Commitments And Contingencies [Line Items]
Lease Term		1 year
Minimum [Member] | Prior Sale Leaseback Transactions [Member]
Commitments And Contingencies [Line Items]
Lease Term		5 years
Maximum [Member]
Commitments And Contingencies [Line Items]
Lease Term		24 years
Maximum [Member] | Prior Sale Leaseback Transactions [Member]
Commitments And Contingencies [Line Items]
Lease Term		24 years