LOANS HELD FOR INVESTMENT - Portfolio Activity (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Change in the activity of loan portfolio
Balance at the beginning of the period			$ 1,726,283,000
Initial funding			247,975,000
Origination fees and discounts, net of costs			(2,929,000)
Additional funding			9,440,000
Amortizing payments			(405,000)
Loan payoffs			(237,702,000)
Origination fee accretion			3,355,000	$ 2,640,000
Balance at the end of the period	$ 1,746,017,000		$ 1,746,017,000
Impairment charges recognized	$ 0	$ 0