Loans and Investments - Risk Ratings and LTV Ratios (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Loans and Investments
Loans and investments, gross	$ 12,249,862	$ 12,615,006
Percentage of Portfolio	100.00%	100.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	2.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	81.00%
Charge-offs, Year One	$ 0	$ 0
Charge-offs, Year Two	0	0
Charge-offs, Year Three	0	0
Charge-offs, Year Four	1,500
Charge-offs, Year Five	0	0
Charge-offs, prior years	0	5,700
Charge-offs, Total	1,500	5,700
Credit risk concentration
Loans and Investments
Origination Year One	193,298	752,918
Origination Year Two	800,883	5,324,481
Origination Year Three	5,165,244	5,581,489
Origination Year Four	5,283,464	488,628
Origination Year Five	342,502	239,648
Origination, Prior Years	464,471	227,842
Loans and investments, gross	$ 12,249,862	$ 12,615,006
Wtd. Avg. First Dollar LTV Ratio (as percent)	2.00%	1.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	81.00%	78.00%
Multifamily | Credit risk concentration
Loans and Investments
Origination Year One	$ 81,630	$ 422,596
Origination Year Two	435,613	4,813,671
Origination Year Three	4,631,723	5,217,946
Origination Year Four	4,969,233	325,426
Origination Year Five	172,926	239,648
Origination, Prior Years	315,323	78,694
Loans and investments, gross	$ 10,606,448	$ 11,097,981
Percentage of Portfolio	87.00%	88.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	2.00%	1.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	84.00%	80.00%
Multifamily | Pass | Credit risk concentration
Loans and Investments
Origination Year One	$ 36,060	$ 80,814
Origination Year Two	92,062	53,316
Origination Year Three	52,027	26,185
Origination Year Four	8,835	2,010
Origination Year Five	2,010	4,598
Origination, Prior Years	24,879	20,300
Loans and investments, gross	215,873	187,223
Multifamily | Pass/Watch | Credit risk concentration
Loans and Investments
Origination Year One	36,501	317,358
Origination Year Two	319,437	2,561,938
Origination Year Three	2,336,702	2,223,155
Origination Year Four	1,846,835	119,860
Origination Year Five	119,860	84,600
Origination, Prior Years	113,100	58,044
Loans and investments, gross	4,772,435	5,364,955
Multifamily | Special Mention | Credit risk concentration
Loans and Investments
Origination Year One	9,069	24,424
Origination Year Two	3,014	1,762,539
Origination Year Three	1,771,071	2,631,689
Origination Year Four	2,787,716	180,750
Origination Year Five	28,250	140,685
Origination, Prior Years	167,229	350
Loans and investments, gross	4,766,349	4,740,437
Multifamily | Substandard | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	21,100	435,878
Origination Year Three	467,123	322,987
Origination Year Four	151,612	8,006
Origination Year Five	8,006	0
Origination, Prior Years	350	0
Loans and investments, gross	648,191	766,871
Multifamily | Doubtful | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	0	0
Origination Year Three	4,800	13,930
Origination Year Four	174,235	14,800
Origination Year Five	14,800	9,765
Origination, Prior Years	9,765	0
Loans and investments, gross	203,600	38,495
Single-Family Rental | Credit risk concentration
Loans and Investments
Origination Year One	111,668	330,322
Origination Year Two	365,270	510,810
Origination Year Three	533,521	363,543
Origination Year Four	314,231	119,692
Origination Year Five	126,066	0
Origination, Prior Years	0	0
Loans and investments, gross	$ 1,450,756	$ 1,324,367
Percentage of Portfolio	12.00%	10.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	0.00%	0.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	63.00%	62.00%
Single-Family Rental | Pass | Credit risk concentration
Loans and Investments
Origination Year One	$ 0	$ 9,709
Origination Year Two	0	608
Origination Year Three	9,476	0
Origination Year Four	9,673	0
Origination Year Five	0	0
Origination, Prior Years	0	0
Loans and investments, gross	19,149	10,317
Single-Family Rental | Pass/Watch | Credit risk concentration
Loans and Investments
Origination Year One	105,172	289,482
Origination Year Two	308,123	465,057
Origination Year Three	446,660	144,846
Origination Year Four	174,652	119,692
Origination Year Five	126,066	0
Origination, Prior Years	0	0
Loans and investments, gross	1,160,673	1,019,077
Single-Family Rental | Special Mention | Credit risk concentration
Loans and Investments
Origination Year One	6,496	31,131
Origination Year Two	57,147	45,145
Origination Year Three	77,385	218,697
Origination Year Four	129,906	0
Origination Year Five	0	0
Origination, Prior Years	0	0
Loans and investments, gross	270,934	294,973
Land | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	8,100
Origination Year Five	8,100	0
Origination, Prior Years	127,928	127,928
Loans and investments, gross	$ 136,028	$ 136,028
Percentage of Portfolio	1.00%	1.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	0.00%	0.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	97.00%	97.00%
Land | Pass/Watch | Credit risk concentration
Loans and Investments
Origination Year One	$ 0	$ 0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	4,600
Origination Year Five	8,100	0
Origination, Prior Years	0	0
Loans and investments, gross	8,100	4,600
Land | Special Mention | Credit risk concentration
Loans and Investments
Origination Year One		0
Origination Year Two		0
Origination Year Three		0
Origination Year Four		3,500
Origination Year Five		0
Origination, Prior Years		0
Loans and investments, gross		3,500
Land | Substandard | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	0
Origination Year Five	0	0
Origination, Prior Years	127,928	127,928
Loans and investments, gross	127,928	127,928
Office | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	35,410
Origination Year Five	35,410	0
Origination, Prior Years	0	0
Loans and investments, gross	$ 35,410	$ 35,410
Percentage of Portfolio	1.00%	1.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	0.00%	0.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	80.00%	80.00%
Office | Special Mention | Credit risk concentration
Loans and Investments
Origination Year One	$ 0	$ 0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	35,410
Origination Year Five	35,410	0
Origination, Prior Years	0	0
Loans and investments, gross	35,410	35,410
Retail | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	0
Origination Year Five	0	0
Origination, Prior Years	19,520	19,520
Loans and investments, gross	$ 19,520	$ 19,520
Percentage of Portfolio	1.00%	1.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	0.00%	0.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	95.00%	88.00%
Retail | Substandard | Credit risk concentration
Loans and Investments
Origination Year One	$ 0	$ 0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	0
Origination Year Five	0	0
Origination, Prior Years	19,520	19,520
Loans and investments, gross	19,520	19,520
Commercial | Credit risk concentration
Loans and Investments
Origination Year One	0	0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	0
Origination Year Five	0	0
Origination, Prior Years	1,700	1,700
Loans and investments, gross	$ 1,700	$ 1,700
Percentage of Portfolio	1.00%	1.00%
Wtd. Avg. First Dollar LTV Ratio (as percent)	63.00%	63.00%
Wtd. Avg. Last Dollar LTV Ratio (as percent)	66.00%	66.00%
Commercial | Doubtful | Credit risk concentration
Loans and Investments
Origination Year One	$ 0	$ 0
Origination Year Two	0	0
Origination Year Three	0	0
Origination Year Four	0	0
Origination Year Five	0	0
Origination, Prior Years	1,700	1,700
Loans and investments, gross	$ 1,700	$ 1,700