Loan Sales and Servicing Activities - Geographical Distribution of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Loan Sales and Servicing Activities
Total loans serviced	$ 284,504,071	$ 245,848,491
California
Loan Sales and Servicing Activities
Total loans serviced	50,009,289	45,621,369
Texas
Loan Sales and Servicing Activities
Total loans serviced	23,023,181	19,741,970
Florida
Loan Sales and Servicing Activities
Total loans serviced	21,006,280	17,490,194
Virginia
Loan Sales and Servicing Activities
Total loans serviced	18,308,994	16,210,673
Maryland
Loan Sales and Servicing Activities
Total loans serviced	13,176,658	11,350,939
All other states
Loan Sales and Servicing Activities
Total loans serviced	$ 158,979,669	$ 135,433,346