Fair Value Accounting - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate carrying amount of impaired loans		$ 107,067		$ 128,874
Impaired loans with an allowance recorded	[1]	(2,630)		(4,658)
Repossessed Assets		52,776	$ 63,759	43,942	$ 57,150
Other assets acquired through foreclosure		$ 52,800		43,900
Collateralized debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities contained credit losses		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans with an allowance recorded		$ (2,600)		(4,700)
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Input Value		5.925%	5.674%
Period of basis point spread		5.30%	5.06%
Percentage of LIBOR		0.63%	0.61%
Junior Subordinated Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Discounted cash flow	Discounted cash flow
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed Assets		$ 52,800
Other assets acquired through foreclosure		52,776		43,942
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate carrying amount of impaired loans		65,246		86,383
Other assets acquired through foreclosure		$ 52,776		$ 43,942
Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Discounted cash flow method		Discounted cash flow method
Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Collateral method		Collateral method
Collateral Method [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Collateral method		Collateral method
Third Party Appraisal [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Third party appraisal		Third party appraisal
Fair Value Measurements, Significant Assumptions		Costs to sell		Costs to sell
Third Party Appraisal [Member] | Loans and Finance Receivables [Member] | Minimum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Costs to Sell		4.00%		4.00%
Third Party Appraisal [Member] | Loans and Finance Receivables [Member] | Maximum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Costs to Sell		10.00%		10.00%
Third Party Appraisal [Member] | Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Third party appraisal		Third party appraisal
Fair Value Measurements, Significant Assumptions		Costs to sell		Costs to sell
Third Party Appraisal [Member] | Other Assets [Member] | Minimum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Costs to Sell		4.00%		4.00%
Third Party Appraisal [Member] | Other Assets [Member] | Maximum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Costs to Sell		10.00%		10.00%
Discount Rate [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Discount rate		Discount rate
Fair Value Measurements, Significant Assumptions		Contractual loan rate		Contractual loan rate
Discount Rate [Member] | Loans and Finance Receivables [Member] | Minimum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Contractual Loan Rate		4.00%		4.00%
Discount Rate [Member] | Loans and Finance Receivables [Member] | Maximum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Contractual Loan Rate		7.00%		7.00%
Scheduled Cash Collections [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Scheduled cash collections		Scheduled cash collections
Fair Value Measurements, Significant Assumptions		Loss given default		Loss given default
Scheduled Cash Collections [Member] | Loans and Finance Receivables [Member] | Minimum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Loss Given Default Rate		0.00%		0.00%
Scheduled Cash Collections [Member] | Loans and Finance Receivables [Member] | Maximum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Loss Given Default Rate		20.00%		20.00%
Proceeds from Non-Real Estate Collateral [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Valuation Technique		Proceeds from non-real estate collateral		Proceeds from non-real estate collateral
Fair Value Measurements, Significant Assumptions		Loss given default		Loss given default
Proceeds from Non-Real Estate Collateral [Member] | Loans and Finance Receivables [Member] | Minimum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Loss Given Default Rate		0.00%		0.00%
Proceeds from Non-Real Estate Collateral [Member] | Loans and Finance Receivables [Member] | Maximum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Loss Given Default Rate		70.00%		70.00%

[1] Includes valuation allowance related to TDR loans of $0.7 million and $0.3 million at March 31, 2016 and December 31, 2015, respectively.