SECURITIES - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale of Available-for-sale Securities, Debt	$ 10,416,000	$ 0
Available-for-sale Securities, Gross Realized Gains	100,000
Available-for-sale Securities, Gross Realized Losses	$ 11,000
Collateral Underlying Mortgage Investments Terms	30- and 15-year fixed and 10/1 adjustable rate mortgage
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	$ 16,600,000
Cost Method Investments, Fair Value Disclosure	16,600,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	468,915,000			$ 698,059,000
Accumulated unrealized losses	12,271,000			$ 12,703,000
Securities Available For Sale Transferred To Held-To-Maturity	49,100,000		$ 158,800,000
Available For Sale Securities Transferred To Held To Maturity Securities Unrealized Gain Loss	2,300,000		$ 3,100,000
Trading Securities, Unrealized Holding Loss	$ 2,300,000
Common Stock, Shares, Outstanding	37,922,250			34,351,409
Debt Instrument, Convertible, Conversion Price	$ 1.6483
Common Class B [Member]
Schedule of Available-for-sale Securities [Line Items]
Common Stock, Shares, Outstanding	11,330
Common Class A [Member]
Schedule of Available-for-sale Securities [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities	18,675
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments, Total	$ 1,400,000
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	800,000
Carrying Amount [Member] | Repurchase Agreement [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	198,300,000
Carrying Amount [Member] | United States Treasury Deposits and Other Public and Trust Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	169,600,000
Fair Value [Member] | United States Treasury Deposits and Other Public and Trust Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	165,000,000
Mortgage Backed Securities And Collateralized Mortgage Obligations Of Us Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	167,300,000
Accumulated unrealized losses	1,900,000
Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	158,700,000
Accumulated unrealized losses	7,200,000
Private Collateralized Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	93,800,000
Accumulated unrealized losses	$ 2,400,000