Freestanding Derivative Financial Instruments - Schedule of Notional or Contractual Amounts and Fair Values of Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Total derivative instruments, Assets, Fair Value	$ 100,735	$ 68,151
Fair Value, Derivative Assets, Cash Margin	12,421	14,664
Total derivative instruments, Liabilities, Fair Value	37,937	30,024
Fair Value, Derivative Liabilities, Cash Margin	4,459	2,780
Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Notional/ Contractual Amount	4,681,594	2,825,924
Fair Value, Derivative Assets	84,925	60,400
Fair Value, Derivative Liabilities	204	263
Forward Sales Commitments [Member]
Derivative [Line Items]
Notional/ Contractual Amount	7,123,500	4,989,400
Fair Value, Derivative Assets	1,383	332
Fair Value, Derivative Liabilities	37,729	29,744
MBS Purchase Commitments [Member]
Derivative [Line Items]
Notional/ Contractual Amount	2,660,756	1,847,000
Fair Value, Derivative Assets	14,427	7,419
Fair Value, Derivative Liabilities	$ 4	$ 17