Significant Accounting Policies and Recently Issued Accounting Pronouncement - (Details) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 02, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recently Issued Accounting Pronouncements
Mortgage servicing rights	$ 2,820,612,000	$ 2,785,964,000	$ 2,486,157,000	$ 2,354,489,000			$ 2,119,588,000	$ 2,016,485,000	$ 1,951,599,000	$ 1,725,061,000
Income taxes payable	400,546,000						52,160,000
Stockholders' equity	$ 1,653,791,000	$ 1,916,710,000	$ 1,861,944,000	$ 1,794,199,000			$ 1,719,674,000	$ 1,590,291,000	$ 1,511,252,000	$ 1,457,595,000	$ 1,399,356,000	$ 1,062,350,000
Adjustment | Accounting Standards Codification 250 Mortgage Servicing Rights Fair Value
Recently Issued Accounting Pronouncements
Mortgage servicing rights						$ 848,000
Income taxes payable					$ 72,000
Stockholders' equity					$ 776,000