SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASU 2016-13 (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Allowance for risk-sharing obligations	$ 70,495	$ 69,191	$ 11,471	$ 7,256	$ 7,964	$ 4,622
Retained earnings	$ 883,049		$ 796,775