SEGMENTS - Product Concentration (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Product concentration
Purchased servicing portfolio loans final unpaid principal balance	$ 63,081,154	$ 59,121,989	$ 57,321,824	$ 51,040,752	$ 50,212,264	$ 47,794,561	$ 47,713,739	$ 46,066,660	$ 44,031,890
Fannie Mae
Product concentration
Purchased servicing portfolio loans final unpaid principal balance	27,728,164				22,915,088				20,521,425
Freddie Mac
Product concentration
Purchased servicing portfolio loans final unpaid principal balance	20,688,410				17,810,007				12,916,705
Ginnie Mae-HUD
Product concentration
Purchased servicing portfolio loans final unpaid principal balance	9,155,794				5,657,809				5,828,981
Life insurance companies and other
Product concentration
Purchased servicing portfolio loans final unpaid principal balance	$ 5,508,786				$ 3,829,360				$ 4,764,779