Derivative Instruments and Other Hedging Activities - Effect of Derivatives Not Designated as Hedging Instruments on Consolidated Financial Statements (Detail) (Not Designated as Hedging Instruments [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 1,520	$ (634)
Interest Rate Contracts [Member] | Other Income (Expense) [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	1,005	538
Forward Sale Contracts [Member] | Mortgage Income [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(253)	(3,005)
Written and Purchased Options [Member] | Mortgage Income [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 768	$ 1,833