SECURITIES - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2014	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale of Available-for-sale Securities, Debt	$ 3,700,000		$ 26,800,000	$ 7,525,000	$ 39,047,000
Available-for-sale Securities, Gross Realized Gains	15,000		301,000	36,000	448,000
Available-for-sale Securities, Gross Realized Losses	62,000		$ 76,000	62,000	$ 87,000
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	38,600,000			38,600,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	624,062,000			624,062,000			$ 862,873,000
Accumulated unrealized losses	9,816,000			9,816,000			18,443,000
Securities Available For Sale Transferred To Held-To-Maturity				60,100,000		$ 158,800,000
Available For Sale Securities Transferred To Held To Maturity Securities Unrealized Gain Loss				3,100,000		$ 3,100,000
Trading Securities, Unrealized Holding Loss				1,500,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	249,413,000			249,413,000			664,476,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,537,000			2,537,000			13,451,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	374,649,000			374,649,000			198,397,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 7,279,000			$ 7,279,000			$ 4,992,000
Common Stock, Shares, Outstanding	43,512,179			43,512,179			38,021,835
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments, Total		$ 6,200,000
Common Class B [Member]
Schedule of Available-for-sale Securities [Line Items]
Common Stock, Shares, Outstanding	11,330	211,330		11,330
Stock Issued During Period, Shares, Conversion of Convertible Securities		200,000
Common Class A [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Instrument, Convertible, Conversion Price		$ 1.6483
Stock Issued During Period, Shares, Conversion of Convertible Securities		348,335
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,500,000			$ 1,500,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	6,600,000			6,600,000			$ 22,800,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	100,000			100,000			400,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value							$ 13,100,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	200,000			200,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0			0
Carrying Amount [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	178,300,000			178,300,000
Carrying Amount [Member] | Repurchase Agreement [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	142,200,000			142,200,000
Private Collateralized Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	542,000,000			542,000,000
Accumulated unrealized losses	8,800,000			8,800,000
Seasoned Residential Collateral Of Us Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	22,000,000			22,000,000
Accumulated unrealized losses	$ 400,000			$ 400,000