Summary of Notes Payable, Secured Revolving Repurchase Agreements, Senior Secured Credit Facility (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Index Rate	one-month LIBOR
Commitment Amount	$ 3,610,303	$ 3,376,158
Maximum Current Availability	1,408,923	1,250,870
Balance Outstanding	2,201,380	2,125,288
Principal Balance of Collateral	3,237,096	3,192,866
Repurchase Agreements
Debt Instrument [Line Items]
Commitment Amount	2,841,642	2,726,942
Maximum Current Availability	1,193,184	891,141
Balance Outstanding	1,648,458	1,835,801
Principal Balance of Collateral	2,474,090	2,762,214
Senior Secured Credit Facilities
Debt Instrument [Line Items]
Commitment Amount	660,000
Maximum Current Availability	208,416
Balance Outstanding	451,584
Principal Balance of Collateral	619,666
Notes Payable
Debt Instrument [Line Items]
Commitment Amount	108,661	399,216
Maximum Current Availability	7,323	109,729
Balance Outstanding	101,338	289,487
Principal Balance of Collateral	$ 143,340	$ 430,652
Debt Instrument, Interest Rate at 3.6% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		Dec. 09, 2019
Index Rate		1 Month Libor
Weighted Average Spread		2.00%
Interest Rate		3.60%
Commitment Amount		$ 150,000
Maximum Current Availability		78,600
Balance Outstanding		71,400
Principal Balance of Collateral		$ 93,000
Bank of the Ozarks \| Debt Instrument, Interest Rate at 5.8% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date	Aug. 23, 2019
Index Rate	1 Month Libor
Weighted Average Spread	4.50%
Interest Rate	5.80%
Commitment Amount	$ 76,161
Maximum Current Availability	7,323
Balance Outstanding	68,838
Principal Balance of Collateral	$ 98,340
Bank of the Ozarks \| Debt Instrument, Interest Rate at 5.9% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date		Aug. 23, 2019
Index Rate		1 Month Libor
Weighted Average Spread		4.50%
Interest Rate		5.90%
Commitment Amount		$ 92,400
Maximum Current Availability		43,979
Balance Outstanding		48,421
Principal Balance of Collateral		$ 69,172
Bank of the Ozarks \| Debt Instrument, Interest Rate at 5.4% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date		Aug. 31, 2018
Index Rate		1 Month Libor
Weighted Average Spread		4.00%
Interest Rate		5.40%
Commitment Amount		$ 68,600
Maximum Current Availability		14,151
Balance Outstanding		54,449
Principal Balance of Collateral		$ 77,784
Bank of the Ozarks \| Debt Instrument, Interest Rate at 6.1% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date		May 22, 2018
Index Rate		1 Month Libor
Weighted Average Spread		4.80%
Interest Rate		6.10%
Commitment Amount		$ 48,750
Maximum Current Availability		17,479
Balance Outstanding		31,271
Principal Balance of Collateral		$ 48,109
Deutsche Bank \| Debt Instrument, Interest Rate at 4.9% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date		Sep. 25, 2019
Index Rate		1 Month Libor
Weighted Average Spread		3.50%
Interest Rate		4.90%
Commitment Amount		$ 64,779
Maximum Current Availability		15,895
Balance Outstanding		48,884
Principal Balance of Collateral		$ 81,473
Deutsche Bank \| Debt Instrument, Interest Rate at 4.6% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date		Jun. 29, 2018
Index Rate		1 Month Libor
Weighted Average Spread		3.30%
Interest Rate		4.60%
Commitment Amount		$ 49,644
Maximum Current Availability		18,224
Balance Outstanding		31,420
Principal Balance of Collateral		$ 48,339
Deutsche Bank \| Debt Instrument, Interest Rate at 5.0% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date		Dec. 09, 2018
Index Rate		1 Month Libor
Weighted Average Spread		3.70%
Interest Rate		5.00%
Commitment Amount		$ 42,543
Maximum Current Availability		1
Balance Outstanding		42,542
Principal Balance of Collateral		$ 60,775
BMO Harris Bank \| Debt Instrument, Interest Rate at 4.0% \| Notes Payable
Debt Instrument [Line Items]
Maturity Date	Apr. 09, 2020	Apr. 09, 2020
Index Rate	1 Month Libor	1 Month Libor
Weighted Average Spread	2.70%	2.70%
Interest Rate	4.00%	4.00%
Commitment Amount	$ 32,500	$ 32,500
Balance Outstanding	32,500	32,500
Principal Balance of Collateral	$ 45,000	$ 45,000
Goldman Sachs \| Debt Instrument, Interest Rate at 4.4% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date	Aug. 19, 2019
Index Rate	1 Month Libor
Weighted Average Spread	2.30%
Interest Rate	4.40%
Commitment Amount	$ 750,000
Maximum Current Availability	378,430
Balance Outstanding	371,570
Principal Balance of Collateral	$ 780,647
Goldman Sachs \| Debt Instrument, Interest Rate at 2.5% \| CMBS \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date	Dec. 03, 2018
Index Rate	3 Month Libor
Weighted Average Spread	0.20%
Interest Rate	2.50%
Commitment Amount	$ 100,000
Maximum Current Availability	65,226
Balance Outstanding	34,774
Principal Balance of Collateral	$ 38,710
Goldman Sachs \| Debt Instrument, Interest Rate at 3.6% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		Aug. 19, 2018
Index Rate		1 Month Libor
Weighted Average Spread		2.20%
Interest Rate		3.60%
Commitment Amount		$ 750,000
Maximum Current Availability		183,253
Balance Outstanding		566,747
Principal Balance of Collateral		$ 890,736
Goldman Sachs \| Debt Instrument, Interest Rate at 1.6% \| CMBS \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		Mar. 02, 2018
Index Rate		3 Month Libor
Weighted Average Spread		0.10%
Interest Rate		1.60%
Commitment Amount		$ 100,000
Maximum Current Availability		64,615
Balance Outstanding		35,385
Principal Balance of Collateral		$ 39,332
Wells Fargo \| Debt Instrument, Interest Rate at 4.1% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date	May 25, 2019
Index Rate	1 Month Libor
Weighted Average Spread	1.90%
Interest Rate	4.10%
Commitment Amount	$ 750,000
Maximum Current Availability	305,988
Balance Outstanding	444,012
Principal Balance of Collateral	$ 600,575
Wells Fargo \| Debt Instrument, Interest Rate at 3.6% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		May 25, 2019
Index Rate		1 Month Libor
Weighted Average Spread		2.10%
Interest Rate		3.60%
Commitment Amount		$ 750,000
Maximum Current Availability		232,462
Balance Outstanding		517,538
Principal Balance of Collateral		$ 814,886
JP Morgan \| Debt Instrument, Interest Rate at 4.0% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		Aug. 20, 2018
Index Rate		1 Month Libor
Weighted Average Spread		2.50%
Interest Rate		4.00%
Commitment Amount		$ 376,942
Maximum Current Availability		120,014
Balance Outstanding		256,928
Principal Balance of Collateral		$ 382,135
JP Morgan \| Debt Instrument, Interest Rate at 4.2% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date	Aug. 20, 2021
Index Rate	1 Month Libor
Weighted Average Spread	2.10%
Interest Rate	4.20%
Commitment Amount	$ 428,802
Maximum Current Availability	91,486
Balance Outstanding	337,316
Principal Balance of Collateral	$ 455,267
Morgan Stanley \| Debt Instrument, Interest Rate at 4.5% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date	May 04, 2019
Index Rate	1 Month Libor
Weighted Average Spread	2.30%
Interest Rate	4.50%
Commitment Amount	$ 500,000
Maximum Current Availability	245,254
Balance Outstanding	254,746
Principal Balance of Collateral	$ 337,591
Morgan Stanley \| Debt Instrument, Interest Rate at 3.9% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		May 04, 2019
Index Rate		1 Month Libor
Weighted Average Spread		2.40%
Interest Rate		3.90%
Commitment Amount		$ 500,000
Maximum Current Availability		120,002
Balance Outstanding		379,998
Principal Balance of Collateral		$ 533,707
US Bank \| Debt Instrument, Interest Rate at 4.0% \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date	Oct. 09, 2021
Index Rate	1 Month Libor
Weighted Average Spread	1.80%
Interest Rate	4.00%
Commitment Amount	$ 212,840
Maximum Current Availability	6,800
Balance Outstanding	206,040
Principal Balance of Collateral	$ 261,300
Royal Bank of Canada \| CMBS \| Repurchase Agreements
Debt Instrument [Line Items]
Index Rate	3 Month Libor
Commitment Amount	$ 100,000
Maximum Current Availability	$ 100,000
Royal Bank of Canada \| Debt Instrument, Interest Rate at 2.6% \| CMBS \| Repurchase Agreements
Debt Instrument [Line Items]
Maturity Date		Mar. 20, 2018
Index Rate		3 Month Libor
Weighted Average Spread		1.00%
Interest Rate		2.60%
Commitment Amount		$ 100,000
Maximum Current Availability		92,195
Balance Outstanding		7,805
Principal Balance of Collateral		$ 8,418
Bank of America \| Senior Secured Credit Facilities
Debt Instrument [Line Items]
Maturity Date	Sep. 29, 2020	Sep. 29, 2020
Index Rate	1 Month Libor	1 Month Libor
Weighted Average Spread	1.90%
Interest Rate	4.10%
Commitment Amount	$ 500,000	$ 250,000
Maximum Current Availability	112,560	250,000
Balance Outstanding	387,440	$ 0
Principal Balance of Collateral	$ 486,666
Bank of America \| Debt Instrument, Interest Rate at 4.1% \| Senior Secured Credit Facilities
Debt Instrument [Line Items]
Maturity Date	Sep. 29, 2020
Index Rate	1 Month Libor
Weighted Average Spread	1.90%
Interest Rate	4.10%
Commitment Amount	$ 500,000
Maximum Current Availability	112,560
Balance Outstanding	$ 387,440
Citibank \| Debt Instrument, Interest Rate at 4.5% \| Senior Secured Credit Facilities
Debt Instrument [Line Items]
Maturity Date	Jul. 12, 2020
Index Rate	1 Month Libor
Weighted Average Spread	2.30%
Interest Rate	4.50%
Commitment Amount	$ 160,000
Maximum Current Availability	95,856
Balance Outstanding	64,144
Principal Balance of Collateral	$ 133,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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- Definition

Amount of assets pledged to secure a debt instrument.

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Weighted average interest rate of debt outstanding.

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