FAIR VALUE MEASUREMENTS - Schedule of Carrying Amounts and the Fair Values of the Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial assets:
Cash and cash equivalents	$ 85,363	$ 118,756	$ 83,887	$ 136,988
Restricted cash	17,179	9,861	14,370	5,306
Pledged securities	95,102	84,850	$ 81,933	$ 72,190
Loans held for sale	3,275,761	1,858,358
Loans held for investment, net	152,050	220,377
Derivative assets	43,853	61,824
Financial liabilities:
Derivative liabilities	175	4,396
Warehouse notes payable	3,305,589	1,990,183
Note payable	163,935	164,163
Carrying Amount
Financial assets:
Cash and cash equivalents	85,363	118,756
Restricted cash	17,179	9,861
Pledged securities	95,102	84,850
Loans held for sale	3,275,761	1,858,358
Loans held for investment, net	152,050	220,377
Derivative assets	43,853	61,824
Total financial assets	3,669,308	2,354,026
Financial liabilities:
Derivative liabilities	175	4,396
Warehouse notes payable	3,305,589	1,990,183
Note payable	163,935	164,163
Total financial liabilities	3,469,699	2,158,742
Fair Value
Financial assets:
Cash and cash equivalents	85,363	118,756
Restricted cash	17,179	9,861
Pledged securities	95,102	84,850
Loans held for sale	3,275,761	1,858,358
Loans held for investment, net	152,764	222,313
Derivative assets	43,853	61,824
Total financial assets	3,670,022	2,355,962
Financial liabilities:
Derivative liabilities	175	4,396
Warehouse notes payable	3,305,807	1,992,111
Note payable	166,499	167,327
Total financial liabilities	$ 3,472,481	$ 2,163,834