FAIR VALUE MEASUREMENTS - Schedule of Carrying Amounts and the Fair Values of the Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Financial assets:
Cash and cash equivalents	$ 81,531	$ 191,218	$ 53,338	$ 118,756
Restricted cash	29,986	6,677	15,768	9,861
Pledged securities	105,803	97,859	$ 92,401	$ 84,850
Loans held for sale	1,257,256	951,829
Loans held for investment, net	130,397	66,510
Derivative assets	26,632	10,357
Financial liabilities:
Derivative liabilities	8,669	1,850
Warehouse notes payable	1,250,642	937,769
Note payable	163,704	163,858
Carrying Amount
Financial assets:
Cash and cash equivalents	81,531	191,218
Restricted cash	29,986	6,677
Pledged securities	105,803	97,859
Loans held for sale	1,257,256	951,829
Loans held for investment, net	130,397	66,510
Derivative assets	26,632	10,357
Total financial assets	1,631,605	1,324,450
Financial liabilities:
Derivative liabilities	8,669	1,850
Warehouse notes payable	1,250,642	937,769
Note payable	163,704	163,858
Total financial liabilities	1,423,015	1,103,477
Fair Value
Financial assets:
Cash and cash equivalents	81,531	191,218
Restricted cash	29,986	6,677
Pledged securities	105,803	97,859
Loans held for sale	1,257,256	951,829
Loans held for investment, net	131,029	66,963
Derivative assets	26,632	10,357
Total financial assets	1,632,237	1,324,903
Financial liabilities:
Derivative liabilities	8,669	1,850
Warehouse notes payable	1,252,059	939,500
Note payable	165,671	166,223
Total financial liabilities	$ 1,426,399	$ 1,107,573