Mortgage Servicing Rights and Mortgage Servicing Liabilities - Activity in MSRs at Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017
Activity in MSRs carried at fair value
Balance at beginning of year	$ 2,807,333
Change in fair value due to:
Balance at end of year	2,920,603	$ 2,807,333
Mortgage servicing rights
Activity in MSRs carried at fair value
Balance at beginning of year	2,820,612	638,010	$ 515,925
Reclassification of mortgage servicing rights previously accounted for under the amortization method pursuant to adoption of the fair value method of accounting					$ 1,482,426
Balance after reclassification				$ 2,820,612	$ 2,120,436	$ 515,925
Additions - Resulting from loan sales	884,876	591,757	24,471
Additions - Purchases	227,445	237,803	183,850
Additions	1,112,321	829,560	208,321
Change in fair value due to:
Changes in inputs used in valuation model	(550,666)	174,458	(4,771)
Other changes in fair value	(455,477)	(303,842)	(81,465)
Total change in fair value	(1,006,143)	(129,384)	(86,236)
Balance at end of year	2,926,790	2,820,612	$ 638,010
Fair value of mortgage servicing rights pledged to secure Assets sold under agreements to repurchase and Notes payable	$ 2,920,603	$ 2,807,333