Mortgage Servicing Rights and Mortgage Servicing Liabilities - Activity in MSRs at Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Jan. 01, 2017	Jan. 01, 2016
Activity in MSRs carried at fair value
Balance at beginning of year	$ 638,010
Change in fair value:
Balance at end of year	2,820,612	$ 638,010
Mortgage servicing rights
Activity in MSRs carried at fair value
Balance at beginning of year	638,010	515,925	$ 660,247
Reclassification of mortgage servicing rights previously accounted for under the amortization method				$ 1,482,426
Balance after reclassification				$ 2,120,436	$ 515,925	$ 660,247
Additions - Purchases	237,803	183,850	146
Additions - Mortgage servicing rights resulting from mortgage loan sales	591,757	24,471	17,319
Additions	829,560	208,321	17,465
Change in fair value:
Changes in inputs used in valuation model	174,458	(4,771)	(80,244)
Other changes in fair value	(303,842)	(81,465)	(81,543)
Total change in fair value	(129,384)	(86,236)	(161,787)
Balance at end of year	2,820,612	638,010	$ 515,925
Total	$ 2,807,333	$ 630,711