Goodwill and Other Intangible Assets - Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 120,854		$ 123,439
Accumulated Amortization	(85,154)		(84,072)
Valuation Allowance	(676)	(592)
Net Intangible Assets	35,024		38,775
Loan Servicing Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	73,096		72,154
Accumulated Amortization	(53,597)		(51,708)
Valuation Allowance	(676)	(592)
Net Intangible Assets	18,823		19,854
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	43,384		46,694
Accumulated Amortization	(29,219)		(29,916)
Valuation Allowance	0	0
Net Intangible Assets	14,165		16,778
Other [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	4,374		4,591
Accumulated Amortization	(2,338)		(2,448)
Valuation Allowance	0	0
Net Intangible Assets	$ 2,036		$ 2,143