Loan Sales and Servicing Activities - Geographical Distribution of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Loan Sales and Servicing Activities
Total loans serviced	$ 299,293,872	$ 245,848,491
California
Loan Sales and Servicing Activities
Total loans serviced	51,377,441	45,621,369
Texas
Loan Sales and Servicing Activities
Total loans serviced	23,648,042	19,741,970
Florida
Loan Sales and Servicing Activities
Total loans serviced	22,650,926	17,490,194
Virginia
Loan Sales and Servicing Activities
Total loans serviced	19,011,950	16,210,673
Maryland
Loan Sales and Servicing Activities
Total loans serviced	13,774,011	11,350,939
All other states
Loan Sales and Servicing Activities
Total loans serviced	$ 168,831,502	$ 135,433,346