SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Statement of Cash Flows (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents
Cash and cash equivalents	$ 85,363	$ 118,756	$ 83,887	$ 136,988
Restricted cash	17,179	9,861	14,370	5,306
Pledged securities, at fair value	95,102	84,850	81,933	72,190
Total cash, cash equivalents, restricted cash, and restricted cash equivalents	$ 197,644	$ 213,467	$ 180,190	$ 214,484