Fair Value - Key Assumptions Used in Determining Fair Value of MSRs at Time of Initial Recognition (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost, MSR recognized	$ 32,862,000	$ 25,554,000
Amortized cost, UPB of underlying mortgage loans	$ 2,759,545,000	$ 2,282,756,000
Amortized cost, Weighted-average annual servicing fee rate (in basis points)	25.00%	26.00%
Fair value, MSR recognized	$ 3,300,000	$ 1,906,000
Fair value, UPB of underlying mortgage loans	$ 327,025,000	$ 223,653,000
Fair value, Weighted-average annual servicing fee rate (in basis points)	0.26%	0.26%	0.25%
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost, Pricing spread during period	7.20%	6.80%
Amortized cost, Life (in years)	1 year 4 months 24 days	1 year 3 months 18 days
Amortized cost, Annual prepayment speed during period	3.60%	7.60%
Amortized cost, Annual per loan cost of servicing during period	$ 68,000	$ 62,000
Fair value inputs, Pricing spread during period	7.20%	10.30%
Fair value inputs, Weighted average life during period	2 years 3 months 18 days	2 years 7 months 6 days
Fair value inputs, Annual prepayment speed during period	7.20%	8.60%
Fair value inputs, Annual per loan cost of servicing during period	$ 68,000	$ 62,000
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost, Pricing spread during period	10.20%	17.50%
Amortized cost, Life (in years)	12 years 3 months 18 days	7 years 8 months 12 days
Amortized cost, Annual prepayment speed during period	49.20%	51.00%
Amortized cost, Annual per loan cost of servicing during period	$ 68,000	$ 134,000
Fair value inputs, Pricing spread during period	7.20%	14.30%
Fair value inputs, Weighted average life during period	9 years 4 months 24 days	7 years 2 months 12 days
Fair value inputs, Annual prepayment speed during period	34.80%	33.30%
Fair value inputs, Annual per loan cost of servicing during period	$ 68,000	$ 62,000
Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost, Pricing spread during period	7.20%	8.60%
Amortized cost, Life (in years)	7 years	6 years 6 months
Amortized cost, Annual prepayment speed during period	10.40%	9.30%
Amortized cost, Annual per loan cost of servicing during period	$ 68,000	$ 63,000
Fair value inputs, Pricing spread during period	7.20%	11.00%
Fair value inputs, Weighted average life during period	5 years 7 months 6 days	5 years 10 months 24 days
Fair value inputs, Annual prepayment speed during period	15.70%	13.80%
Fair value inputs, Annual per loan cost of servicing during period	$ 68,000	$ 62,000