Investments, Debt and Equity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	$ 5,486,206	$ 5,293,918
Unrealized Gains	158,065	103,156
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(1,744)	(16,421)
Debt Securities, Held-to-maturity, Fair Value	5,642,527	5,380,653
Allowance for credit losses on investment securities held-to-maturity	312	0
Net Carrying Value	5,485,894	5,293,918
Interest Receivable	61,500	59,000
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Interest Receivable	18,300	21,800
Agency CMO [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	156,087	167,443
Unrealized Gains	4,738	1,123
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	0	(1,200)
Debt Securities, Held-to-maturity, Fair Value	160,825	167,366
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	156,087	167,443
Agency MBS [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	2,896,651	2,957,900
Unrealized Gains	95,436	60,602
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(253)	(8,733)
Debt Securities, Held-to-maturity, Fair Value	2,991,834	3,009,769
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	2,896,651	2,957,900
Agency Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	1,450,800	1,172,491
Unrealized Gains	21,003	6,444
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(623)	(5,615)
Debt Securities, Held-to-maturity, Fair Value	1,471,180	1,173,320
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	1,450,800	1,172,491
Municipal Bonds [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	739,531	740,431
Unrealized Gains	35,184	32,709
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(86)	(21)
Debt Securities, Held-to-maturity, Fair Value	774,629	773,119
Allowance for credit losses on investment securities held-to-maturity	312	0
Net Carrying Value	739,219	740,431
Non-agency CMBS [Member]
Schedule of Investments [Line Items]
Investment securities held-to-maturity, net	243,137	255,653
Unrealized Gains	1,704	2,278
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(782)	(852)
Debt Securities, Held-to-maturity, Fair Value	244,059	257,079
Allowance for credit losses on investment securities held-to-maturity	0	0
Net Carrying Value	$ 243,137	$ 255,653