Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) (Not Designated as Hedging Instruments [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	$ 1,130,568	$ 823,180
Derivative Liability, Notional Amount	1,231,363	1,062,436
Forward Sales Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	139,339	15,897
Derivative Liability, Notional Amount	514,645	391,992
Interest Rate Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	502,020	444,703
Derivative Liability, Notional Amount	502,020	444,703
Written and Purchased Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Notional Amount	489,209	362,580
Derivative Liability, Notional Amount	214,698	225,741
Other Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Fair Value	41,120	32,903
Other Assets [Member] | Forward Sales Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Fair Value	1,125	25
Other Assets [Member] | Interest Rate Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Fair Value	19,970	15,434
Other Assets [Member] | Written and Purchased Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Fair Value	20,025	17,444
Other Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Fair Value	35,704	31,354
Other Liabilities [Member] | Forward Sales Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Fair Value	3,910	2,556
Other Liabilities [Member] | Interest Rate Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Fair Value	19,970	15,434
Other Liabilities [Member] | Written and Purchased Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Fair Value	$ 11,824	$ 13,364