LOANS RECEIVABLE, NET - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased student loans		$ 134,000
Commercial real estate loans secured by hotel properties	$ 110,200		$ 65,400
Commercial real estate loans secured by multi-family properties	156,400		112,600
Non-accruing loans	685		83
Accruing loans delinquent 90 days or more	36,900		$ 1,000
Gross interest income	0
Iowa and South Dakota [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased student loans	123,700
Iowa, North Dakota and South Dakota [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total purchased loans secured by properties	$ 10,700