Fair Value Measurements - Schedule of Carrying Amounts and the Fair Values of the Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Financial assets:
Cash and cash equivalents	$ 83,887	$ 136,988	$ 60,163	$ 113,354
Restricted cash	14,370	5,306
Pledged securities	81,933	72,190
Loans held for sale	1,299,028	2,499,111
Loans held for investment, net	261,915	231,493
Derivative assets	33,796	11,678
Financial liabilities:
Derivative liabilities	2,918	1,333
Warehouse notes payable	1,440,425	2,649,470
Note payable	164,238	164,462
Carrying Amount
Financial assets:
Cash and cash equivalents	83,887	136,988
Restricted cash	14,370	5,306
Pledged securities	81,933	72,190
Loans held for sale	1,299,028	2,499,111
Loans held for investment, net	261,915	231,493
Derivative assets	33,796	11,678
Total financial assets	1,774,929	2,956,766
Financial liabilities:
Derivative liabilities	2,918	1,333
Warehouse notes payable	1,440,425	2,649,470
Note payable	164,238	164,462
Total financial liabilities	1,607,581	2,815,265
Fair Value
Financial assets:
Cash and cash equivalents	83,887	136,988
Restricted cash	14,370	5,306
Pledged securities	81,933	72,190
Loans held for sale	1,299,028	2,499,111
Loans held for investment, net	264,508	233,370
Derivative assets	33,796	11,678
Total financial assets	1,777,522	2,958,643
Financial liabilities:
Derivative liabilities	2,918	1,333
Warehouse notes payable	1,441,770	2,652,011
Note payable	167,602	168,431
Total financial liabilities	$ 1,612,290	$ 2,821,775