Other Investments - Additional Information (Details) - USD ($) $ in Thousands			3 Months Ended								12 Months Ended
	Jan. 22, 2019	May 01, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2019	Dec. 31, 2015
Investment [Line Items]
Commitment to fund partnership			$ 36,000								$ 57,000
Commitment to fund partnership, funded amount			36,000								36,000
Servicing asset, fair value			300,000								300,000
Interest income			$ 119,725	$ 99,397	$ 82,976	$ 76,619	$ 71,468	$ 62,737	$ 59,224	$ 54,628	378,717	$ 248,057	$ 246,355
Investment fair value changes, net											(25,689)	10,374	(28,574)
Other income, net											$ 12,874	12,436	20,691
Subsequent Event
Investment [Line Items]
Commitment to fund partnership, funded amount														$ 7,000
5 Arches, LLC
Investment [Line Items]
Minority interest, percentage		20.00%	20.00%								20.00%
Payments to acquire equity method investment		$ 10,000
Option to purchase additional equity, term		1 year
Option to purchase additional equity, amount		$ 40,000
Carrying amount of equity method investments			$ 7,000								$ 7,000
Gross income associated with investment											600
Other income, net											400
5 Arches, LLC | Subsequent Event
Investment [Line Items]
Payments to acquire equity method investment	$ 40,000
Option to purchase additional equity, percent	80.00%
Equity method investment, period for contingent consideration	2 years
5 Arches, LLC, Purchase Option
Investment [Line Items]
Carrying amount of equity method investments			4,000								4,000
MSRs
Investment [Line Items]
Servicing asset, fair value			60,281				63,598				60,281	63,598	$ 118,526		$ 191,976
Servicing asset			4,930,000				5,560,000				4,930,000	5,560,000
Servicer advance financing
Investment [Line Items]
Collateral amounts			287,000								287,000
Interest income			1,000
Investment fair value changes, net			(1,000)
Residential Loans
Investment [Line Items]
Servicing asset, fair value			300,468				0				300,468	0
Servicing asset, unpaid principal balance on underlying loan			8,050,000								8,050,000
Excess MSRs
Investment [Line Items]
Servicing asset, fair value			27,312				$ 0				$ 27,312	$ 0
Interest income			1,000
Investment fair value changes, net			$ 2,000