Investment Securities (Available-for-sale Securities with Unrealized Loss) (Details)	9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2021 securities	Sep. 30, 2021	Sep. 30, 2021 contract	Dec. 31, 2020 USD ($) securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	$ 693,464,000				$ 174,804,000
Less than 12 months, unrealized loss	10,724,000				$ 1,925,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		172			51
12 months or more, fair value	37,990,000				$ 11,740,000
12 months or more, unrealized loss	933,000				$ 381,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		18			15
Total unrealized loss position, fair value	731,454,000				$ 186,544,000
Total unrealized loss	11,657,000				2,306,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	0
Available-for-sale Securities, Amortized Cost Basis	1,294,654,000				734,544,000
Gross Unrealized Gains	14,093,000				20,775,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	11,657,000				2,306,000
Available-for-sale investment securities, at fair value (amortized cost of $1,294,654 at September 30, 2021 and $734,544 at December 31, 2020) (a)	1,297,090,000				753,013,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0				0
Securities Investment [Member]
Available-for-sale securities that had an unrealized loss:
Interest Receivable	5,700,000				2,700,000
States and political subdivisions
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	128,402,000				17,651,000
Less than 12 months, unrealized loss	3,007,000				$ 124,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		76			5
12 months or more, fair value	0				$ 0
12 months or more, unrealized loss	0				$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		0			0
Total unrealized loss position, fair value	128,402,000				$ 17,651,000
Total unrealized loss	3,007,000				124,000
Available-for-sale Securities, Amortized Cost Basis	252,706,000				110,401,000
Gross Unrealized Gains	3,220,000				4,642,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3,007,000				124,000
Available-for-sale investment securities, at fair value (amortized cost of $1,294,654 at September 30, 2021 and $734,544 at December 31, 2020) (a)	252,919,000				114,919,000
Residential mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	466,518,000				156,659,000
Less than 12 months, unrealized loss	6,079,000				$ 1,795,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		72			45
12 months or more, fair value	36,160,000				$ 9,892,000
12 months or more, unrealized loss	763,000				$ 229,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		16			13
Total unrealized loss position, fair value	502,678,000				$ 166,551,000
Total unrealized loss	6,842,000				2,024,000
Available-for-sale Securities, Amortized Cost Basis	894,848,000				609,865,000
Gross Unrealized Gains	10,453,000				15,377,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6,842,000				2,024,000
Available-for-sale investment securities, at fair value (amortized cost of $1,294,654 at September 30, 2021 and $734,544 at December 31, 2020) (a)	898,459,000				623,218,000
Commercial mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	48,974,000
Less than 12 months, unrealized loss	1,101,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		17
12 months or more, fair value	0
12 months or more, unrealized loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		0
Total unrealized loss position, fair value	48,974,000
Total unrealized loss	1,101,000
Available-for-sale Securities, Amortized Cost Basis	63,568,000				4,622,000
Gross Unrealized Gains	85,000				161,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,101,000				0
Available-for-sale investment securities, at fair value (amortized cost of $1,294,654 at September 30, 2021 and $734,544 at December 31, 2020) (a)	62,552,000				4,783,000
Bank-issued trust preferred securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	0				494,000
Less than 12 months, unrealized loss	0				$ 6,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		0			1
12 months or more, fair value	1,830,000				$ 1,848,000
12 months or more, unrealized loss	170,000				$ 152,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		2			2
Total unrealized loss position, fair value	1,830,000				$ 2,342,000
Total unrealized loss	170,000				158,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities		2
Available-for-sale Securities, Amortized Cost Basis	4,616,000				4,696,000
Gross Unrealized Gains	233,000				192,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	170,000				158,000
Available-for-sale investment securities, at fair value (amortized cost of $1,294,654 at September 30, 2021 and $734,544 at December 31, 2020) (a)	4,679,000				4,730,000
Mortgage-backed securities, issued by US government sponsored agencies
Available-for-sale securities that had an unrealized loss:
Percentage of mortgage-backed securities in unrealized loss position for more than 12 months			99.00%
Mortgage-backed securities, privately issued
Available-for-sale securities that had an unrealized loss:
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		2		2
Percentage of mortgage-backed securities in unrealized loss position for more than 12 months			1.00%
Fair value within book value			90.00%
U.S. government sponsored agencies
Available-for-sale securities that had an unrealized loss:
Available-for-sale Securities, Amortized Cost Basis	78,916,000				4,960,000
Gross Unrealized Gains	102,000				403,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	537,000				0
Available-for-sale investment securities, at fair value (amortized cost of $1,294,654 at September 30, 2021 and $734,544 at December 31, 2020) (a)	78,481,000				$ 5,363,000
Agency Securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	49,570,000
Less than 12 months, unrealized loss	537,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		7
12 months or more, fair value	0
12 months or more, unrealized loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		0
Total unrealized loss position, fair value	49,570,000
Total unrealized loss	$ 537,000