Debt - Schedule of Repurchase Transactions and Facilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Amount of Collateral	$ 518,672	$ 595,599
Master repurchase agreement
Debt Instrument [Line Items]
Maximum Borrowing Capacity	832,003	916,759
Amount Outstanding	399,340	421,132
Amount of Collateral	$ 518,672	$ 595,599
Percentage of Collateral Coverage	130.00%	141.00%
Interest Rate	1.60%	2.29%
Debt Instrument 1 at 1.41% Interest Rate | Master repurchase agreement | October 5, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 31,326
Amount Outstanding	31,326
Amount of Collateral	$ 37,953
Percentage of Collateral Coverage	121.00%
Interest Rate	1.41%
Debt Instrument 2 at 1.34% Interest Rate | Master repurchase agreement | October 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 7,073
Amount Outstanding	7,073
Amount of Collateral	$ 8,745
Percentage of Collateral Coverage	124.00%
Interest Rate	1.34%
Debt Instrument 3 at 1.34% Interest Rate | Master repurchase agreement | October 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 4,150
Amount Outstanding	4,150
Amount of Collateral	$ 5,057
Percentage of Collateral Coverage	122.00%
Interest Rate	1.34%
Debt Instrument 4 at 1.74% Interest Rate | Master repurchase agreement | October 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 3,343
Amount Outstanding	3,343
Amount of Collateral	$ 4,761
Percentage of Collateral Coverage	142.00%
Interest Rate	1.74%
Debt Instrument 5 at 1.32% Interest Rate | Master repurchase agreement | October 12, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 5,242
Amount Outstanding	5,242
Amount of Collateral	$ 6,572
Percentage of Collateral Coverage	125.00%
Interest Rate	1.32%
Debt Instrument 6 at 1.18% Interest Rate | Master repurchase agreement | October 15, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 5,553
Amount Outstanding	5,553
Amount of Collateral	$ 6,627
Percentage of Collateral Coverage	119.00%
Interest Rate	1.18%
Debt Instrument 7 at 1.18% Interest Rate | Master repurchase agreement | October 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 10,879
Amount Outstanding	10,879
Amount of Collateral	$ 12,889
Percentage of Collateral Coverage	118.00%
Interest Rate	1.18%
Debt Instrument 8 at 1.11% Interest Rate | Master repurchase agreement | October 22, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 7,899
Amount Outstanding	7,899
Amount of Collateral	$ 9,279
Percentage of Collateral Coverage	117.00%
Interest Rate	1.11%
Debt Instrument 9 at 1.11% Interest Rate | Master repurchase agreement | October 22, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 6,231
Amount Outstanding	6,231
Amount of Collateral	$ 7,276
Percentage of Collateral Coverage	117.00%
Interest Rate	1.11%
Debt Instrument 10 at 1.11% Interest Rate | Master repurchase agreement | October 22, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 5,123
Amount Outstanding	5,123
Amount of Collateral	$ 6,063
Percentage of Collateral Coverage	118.00%
Interest Rate	1.11%
Debt Instrument 11 at 1.33% Interest Rate | Master repurchase agreement | October 29, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 9,984
Amount Outstanding	9,984
Amount of Collateral	$ 12,436
Percentage of Collateral Coverage	125.00%
Interest Rate	1.33%
Debt Instrument 12 at 1.33% Interest Rate | Master repurchase agreement | October 29, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 9,840
Amount Outstanding	9,840
Amount of Collateral	$ 11,851
Percentage of Collateral Coverage	120.00%
Interest Rate	1.33%
Debt Instrument 13 at 1.72% Interest Rate | Master repurchase agreement | November 12, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 3,110
Amount Outstanding	3,110
Amount of Collateral	$ 4,428
Percentage of Collateral Coverage	142.00%
Interest Rate	1.72%
Debt Instrument 14 at 1.33% Interest Rate | Master repurchase agreement | November 19, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 9,747
Amount Outstanding	9,747
Amount of Collateral	$ 12,635
Percentage of Collateral Coverage	130.00%
Interest Rate	1.33%
Debt Instrument 15 at 1.73% Interest Rate | Master repurchase agreement | November 24, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 3,543
Amount Outstanding	3,543
Amount of Collateral	$ 5,106
Percentage of Collateral Coverage	144.00%
Interest Rate	1.73%
Debt Instrument 16 at 1.12% Interest Rate | Master repurchase agreement | December 7, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 5,825
Amount Outstanding	5,825
Amount of Collateral	$ 7,444
Percentage of Collateral Coverage	128.00%
Interest Rate	1.12%
Debt Instrument 17 at 1.12% Interest Rate | Master repurchase agreement | December 7, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 2,311
Amount Outstanding	2,311
Amount of Collateral	$ 2,848
Percentage of Collateral Coverage	123.00%
Interest Rate	1.12%
Debt Instrument 18 at 1.35% Interest Rate | Master repurchase agreement | December 13, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 14,148
Amount Outstanding	14,148
Amount of Collateral	$ 20,151
Percentage of Collateral Coverage	142.00%
Interest Rate	1.35%
Debt Instrument 19 at 1.15% Interest Rate | Master repurchase agreement | December 13, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 7,160
Amount Outstanding	7,160
Amount of Collateral	$ 8,682
Percentage of Collateral Coverage	121.00%
Interest Rate	1.15%
Debt Instrument 20 at 1.12% Interest Rate | Master repurchase agreement | December 16, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 44,200
Amount Outstanding	44,200
Amount of Collateral	$ 57,815
Percentage of Collateral Coverage	131.00%
Interest Rate	1.12%
Debt Instrument 21 at 1.37% Interest Rate | Master repurchase agreement | December 16, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 4,333
Amount Outstanding	4,333
Amount of Collateral	$ 6,232
Percentage of Collateral Coverage	144.00%
Interest Rate	1.37%
Debt Instrument 22 at 1.32% Interest Rate | Master repurchase agreement | December 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 7,333
Amount Outstanding	7,333
Amount of Collateral	$ 9,556
Percentage of Collateral Coverage	130.00%
Interest Rate	1.32%
Debt Instrument 23 at 1.32% Interest Rate | Master repurchase agreement | December 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 6,687
Amount Outstanding	6,687
Amount of Collateral	$ 8,451
Percentage of Collateral Coverage	126.00%
Interest Rate	1.32%
Debt Instrument 24 at 1.72% Interest Rate | Master repurchase agreement | December 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 1,179
Amount Outstanding	1,179
Amount of Collateral	$ 1,687
Percentage of Collateral Coverage	143.00%
Interest Rate	1.72%
Debt Instrument 25 at 0.57% Interest Rate | Master repurchase agreement | December 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 35,153
Amount Outstanding	35,153
Amount of Collateral	$ 37,867
Percentage of Collateral Coverage	108.00%
Interest Rate	0.57%
Debt Instrument A at 0.87% Interest Rate | Master repurchase agreement | December 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 2,918
Amount Outstanding	2,918
Amount of Collateral	$ 3,421
Percentage of Collateral Coverage	117.00%
Interest Rate	0.87%
Debt Instrument B at 1.07% Interest Rate | Master repurchase agreement | December 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 1,570
Amount Outstanding	1,570
Amount of Collateral	$ 1,943
Percentage of Collateral Coverage	124.00%
Interest Rate	1.07%
Debt Instrument C at 1.47% Interest Rate | Master repurchase agreement | December 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 1,400
Amount Outstanding	1,400
Amount of Collateral	$ 2,047
Percentage of Collateral Coverage	146.00%
Interest Rate	1.47%
Debt Instrument 26 at 1.32% Interest Rate | Master repurchase agreement | December 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 1,341
Amount Outstanding	1,341
Amount of Collateral	$ 1,788
Percentage of Collateral Coverage	133.00%
Interest Rate	1.32%
Debt Instrument 27 at 1.33% Interest Rate | Master repurchase agreement | December 27, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 16,643
Amount Outstanding	16,643
Amount of Collateral	$ 21,720
Percentage of Collateral Coverage	131.00%
Interest Rate	1.33%
Debt Instrument 28 at 1.73% Interest Rate | Master repurchase agreement | December 27, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 4,482
Amount Outstanding	4,482
Amount of Collateral	$ 6,413
Percentage of Collateral Coverage	143.00%
Interest Rate	1.73%
Debt Instrument 29 at 1.33% Interest Rate | Master repurchase agreement | December 27, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 2,277
Amount Outstanding	2,277
Amount of Collateral	$ 2,923
Percentage of Collateral Coverage	128.00%
Interest Rate	1.33%
Debt Instrument at 2.58% Interest Rate | Master repurchase agreement | July 8, 2022
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 150,000
Amount Outstanding	14,085
Amount of Collateral	$ 21,232
Percentage of Collateral Coverage	151.00%
Interest Rate	2.58%
Debt Instrument D at 2.58% Interest Rate | Master repurchase agreement | September 22, 2022
Debt Instrument [Line Items]
Maximum Borrowing Capacity	$ 400,000
Amount Outstanding	103,252
Amount of Collateral	$ 144,774
Percentage of Collateral Coverage	140.00%
Interest Rate	2.58%
Debt Instrument 30 at 2.33% Interest Rate | Master repurchase agreement | January 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 35,635
Amount Outstanding		35,635
Amount of Collateral		$ 46,120
Percentage of Collateral Coverage		129.00%
Interest Rate		2.33%
Debt Instrument 31 at 2.33% Interest Rate | Master repurchase agreement | January 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 7,697
Amount Outstanding		7,697
Amount of Collateral		$ 10,075
Percentage of Collateral Coverage		131.00%
Interest Rate		2.33%
Debt Instrument 32 at 2.48% Interest Rate | Master repurchase agreement | January 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 6,311
Amount Outstanding		6,311
Amount of Collateral		$ 9,038
Percentage of Collateral Coverage		143.00%
Interest Rate		2.48%
Debt Instrument 33 at 2.33% Interest Rate | Master repurchase agreement | January 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 4,755
Amount Outstanding		4,755
Amount of Collateral		$ 6,114
Percentage of Collateral Coverage		129.00%
Interest Rate		2.33%
Debt Instrument 34 at 2.33% Interest Rate | Master repurchase agreement | January 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 4,666
Amount Outstanding		4,666
Amount of Collateral		$ 6,044
Percentage of Collateral Coverage		130.00%
Interest Rate		2.33%
Debt Instrument 35 at 2.48% Interest Rate | Master repurchase agreement | January 6, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 3,213
Amount Outstanding		3,213
Amount of Collateral		$ 4,667
Percentage of Collateral Coverage		145.00%
Interest Rate		2.48%
Debt Instrument 36 at 2.32% Interest Rate | Master repurchase agreement | January 11, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 5,879
Amount Outstanding		5,879
Amount of Collateral		$ 7,575
Percentage of Collateral Coverage		129.00%
Interest Rate		2.32%
Debt Instrument 37 at 2.35% Interest Rate | Master repurchase agreement | January 14, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 6,991
Amount Outstanding		6,991
Amount of Collateral		$ 8,738
Percentage of Collateral Coverage		125.00%
Interest Rate		2.35%
Debt Instrument 38 at 2.22% Interest Rate | Master repurchase agreement | January 20, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 13,263
Amount Outstanding		13,263
Amount of Collateral		$ 16,582
Percentage of Collateral Coverage		125.00%
Interest Rate		2.22%
Debt Instrument 39 at 2.21% Interest Rate | Master repurchase agreement | January 29, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 7,762
Amount Outstanding		7,762
Amount of Collateral		$ 9,702
Percentage of Collateral Coverage		125.00%
Interest Rate		2.21%
Debt Instrument 40 at 2.21% Interest Rate | Master repurchase agreement | January 29, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 7,153
Amount Outstanding		7,153
Amount of Collateral		$ 9,537
Percentage of Collateral Coverage		133.00%
Interest Rate		2.21%
Debt Instrument 41 at 1.88% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 12,258
Amount Outstanding		12,258
Amount of Collateral		$ 16,052
Percentage of Collateral Coverage		131.00%
Interest Rate		1.88%
Debt Instrument 42 at 1.88% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 12,015
Amount Outstanding		12,015
Amount of Collateral		$ 15,794
Percentage of Collateral Coverage		131.00%
Interest Rate		1.88%
Debt Instrument 43 at 1.88% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 5,298
Amount Outstanding		5,298
Amount of Collateral		$ 6,895
Percentage of Collateral Coverage		130.00%
Interest Rate		1.88%
Debt Instrument 44 at 1.88% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 3,985
Amount Outstanding		3,985
Amount of Collateral		$ 5,136
Percentage of Collateral Coverage		129.00%
Interest Rate		1.88%
Debt Instrument 45 at 1.88% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 2,887
Amount Outstanding		2,887
Amount of Collateral		$ 3,790
Percentage of Collateral Coverage		131.00%
Interest Rate		1.88%
Debt Instrument 46 at 2.03% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 2,332
Amount Outstanding		2,332
Amount of Collateral		$ 3,360
Percentage of Collateral Coverage		144.00%
Interest Rate		2.03%
Debt Instrument 47 at 2.03% Interest Rate | Master repurchase agreement | February 1, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 1,132
Amount Outstanding		1,132
Amount of Collateral		$ 1,607
Percentage of Collateral Coverage		142.00%
Interest Rate		2.03%
Debt Instrument 48 at 2.02% Interest Rate | Master repurchase agreement | February 12, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 2,945
Amount Outstanding		2,945
Amount of Collateral		$ 4,428
Percentage of Collateral Coverage		150.00%
Interest Rate		2.02%
Debt Instrument 49 at 1.78% Interest Rate | Master repurchase agreement | March 5, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 24,946
Amount Outstanding		24,946
Amount of Collateral		$ 33,348
Percentage of Collateral Coverage		134.00%
Interest Rate		1.78%
Debt Instrument 50 at 1.78% Interest Rate | Master repurchase agreement | March 5, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 24,312
Amount Outstanding		24,312
Amount of Collateral		$ 32,571
Percentage of Collateral Coverage		134.00%
Interest Rate		1.78%
Debt Instrument 51 at 1.78% Interest Rate | Master repurchase agreement | March 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 10,219
Amount Outstanding		10,219
Amount of Collateral		$ 13,172
Percentage of Collateral Coverage		129.00%
Interest Rate		1.78%
Debt Instrument 52 at 1.78% Interest Rate | Master repurchase agreement | March 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 8,381
Amount Outstanding		8,381
Amount of Collateral		$ 10,872
Percentage of Collateral Coverage		130.00%
Interest Rate		1.78%
Debt Instrument 53 at 1.78% Interest Rate | Master repurchase agreement | March 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 3,894
Amount Outstanding		3,894
Amount of Collateral		$ 5,193
Percentage of Collateral Coverage		133.00%
Interest Rate		1.78%
Debt Instrument 54 at 1.93% Interest Rate | Master repurchase agreement | March 17, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 1,145
Amount Outstanding		1,145
Amount of Collateral		$ 1,687
Percentage of Collateral Coverage		147.00%
Interest Rate		1.93%
Debt Instrument 55 at 1.94% Interest Rate | Master repurchase agreement | March 24, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 7,016
Amount Outstanding		7,016
Amount of Collateral		$ 10,024
Percentage of Collateral Coverage		143.00%
Interest Rate		1.94%
Debt Instrument 56 at 1.79% Interest Rate | Master repurchase agreement | March 24, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 5,008
Amount Outstanding		5,008
Amount of Collateral		$ 6,637
Percentage of Collateral Coverage		133.00%
Interest Rate		1.79%
Debt Instrument 57 at 1.79% Interest Rate | Master repurchase agreement | March 24, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 2,577
Amount Outstanding		2,577
Amount of Collateral		$ 3,367
Percentage of Collateral Coverage		131.00%
Interest Rate		1.79%
Debt Instrument 58 at 2.35% Interest Rate | Master repurchase agreement | April 9, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 33,084
Amount Outstanding		33,084
Amount of Collateral		$ 43,069
Percentage of Collateral Coverage		130.00%
Interest Rate		2.35%
Debt Instrument 59 at 2.64% Interest Rate | Master repurchase agreement | July 9, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 250,000
Amount Outstanding		53,256
Amount of Collateral		$ 84,337
Percentage of Collateral Coverage		158.00%
Interest Rate		2.64%
Debt Instrument 60 at 2.65% Interest Rate | Master repurchase agreement | September 23, 2021
Debt Instrument [Line Items]
Maximum Borrowing Capacity		$ 400,000
Amount Outstanding		101,117
Amount of Collateral		$ 160,068
Percentage of Collateral Coverage		158.00%
Interest Rate		2.65%