DEBT - Summary of Mortgage Warehouse Borrowings (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Amount Drawn	$ 54,457,000	$ 118,822,000
Secured Debt
Line of Credit Facility [Line Items]
Amount Drawn	54,457,000	118,822,000
Facility Amount	195,000,000	249,000,000
Mortgage borrowings outstanding, collateralized amount	83,800,000	187,000,000
Collateralized amount of restricted short-term investments	1,300,000	1,600,000
Secured Debt | Warehouse A
Line of Credit Facility [Line Items]
Amount Drawn	1,129,000	12,990,000
Facility Amount	$ 45,000,000	$ 39,000,000
Expiration Date		30 days
Secured Debt | Warehouse A | LIBOR
Line of Credit Facility [Line Items]
Interest Rate	1.75%	2.25%
Secured Debt | Warehouse B
Line of Credit Facility [Line Items]
Amount Drawn	$ 16,857,000	$ 41,447,000
Facility Amount	$ 50,000,000	$ 85,000,000
Secured Debt | Warehouse B | LIBOR
Line of Credit Facility [Line Items]
Interest Rate	2.25%	2.25%
Secured Debt | Warehouse C
Line of Credit Facility [Line Items]
Amount Drawn	$ 36,471,000	$ 64,385,000
Facility Amount	$ 100,000,000	$ 125,000,000
Secured Debt | Warehouse C | LIBOR
Line of Credit Facility [Line Items]
Interest Rate	2.375%	2.375%