Investments (Aggregate Values and Unrealized Gains and Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Investment securities available for sale
Available-for-sale Securities, Amortized Cost Basis, Total	$ 7,335,745	$ 6,911,965
Gross unrealized losses	26,484	8,911
Fair value	7,381,083	7,014,243
Investment in marketable equity securities at cost	84,297	84,837
Investment in marketable equity securities, gross unrealized gains	34,415	8,654
Investment in marketable equity securities, gross unrealized losses	172	1,811
Fair value	118,540	91,680
Investment securities held to maturity
Debt Securities, Held-to-maturity, Total	3,394,604	2,816,982
Gross unrealized gains	7,092
Gross unrealized losses	24,611
Fair value	3,377,085	2,838,499
Debt Securities, Available-for-sale, Held-to-maturity and Equity Securities, Cost	10,814,646	9,813,784
Gross unrealized gains	113,329	141,416
Gross unrealized losses	51,267	10,778
Fair value	10,876,708	9,944,422
Investment securities available for sale at cost	7,335,745	6,911,965
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	71,822	111,189
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	26,484	8,911
Debt Securities, Available-for-sale	7,381,083	7,014,243
Interest receivable, available-for-sale debt securities	18,000	17,600
Interest receivable, held-to-maturity debt securities	6,100	5,400
U.S. Treasury
Investment securities held to maturity
Investment securities available for sale at cost		499,832
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax		101
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		0
Debt Securities, Available-for-sale		499,933
Government agency
Investment securities available for sale
Gross unrealized losses	3,747	5,573
Investment securities held to maturity
Investment securities available for sale at cost	824,216	706,241
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,981	723
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3,747	5,573
Debt Securities, Available-for-sale	825,450	701,391
Residential Mortgage Backed Securities
Investment securities available for sale
Gross unrealized losses	14,324	1,310
Investment securities held to maturity
Debt Securities, Held-to-maturity, Total	2,208,496	1,877,692
Gross unrealized gains	6,567	17,689
Gross unrealized losses	12,189	0
Fair value	2,202,874	1,895,381
Investment securities available for sale at cost	4,770,205	4,369,130
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	29,375	70,283
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	14,324	1,310
Debt Securities, Available-for-sale	4,785,256	4,438,103
Commercial Mortgage Backed Securities
Investment securities available for sale
Available-for-sale Securities, Amortized Cost Basis, Total	1,144,024	745,892
Gross unrealized gains	12,702	25,645
Gross unrealized losses	8,196	0
Fair value	1,148,530	771,537
Investment securities held to maturity
Debt Securities, Held-to-maturity, Total	1,184,101	937,034
Gross unrealized gains	525	3,884
Gross unrealized losses	12,422	56
Fair value	1,172,204	940,862
Residential mortgage-backed securities
Investment securities held to maturity
Debt Securities, Held-to-maturity, Total		2,816,982
Gross unrealized gains		21,573
Gross unrealized losses		56
Fair value		2,838,499
Commercial mortgage-backed securities
Investment securities available for sale
Gross unrealized losses	217
Investment securities held to maturity
Investment securities available for sale at cost	597,300	590,870
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	24,764	14,437
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	217	2,028
Debt Securities, Available-for-sale	621,847	603,279
Other
Investment securities held to maturity
Debt Securities, Held-to-maturity, Total	2,007	2,256
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	$ 2,007	$ 2,256

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Interest Receivable, Available-For-Sale Debt Securities

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