Investment Securities (Available-for-sale Securities with Unrealized Loss) (Details)	6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2021 securities	Jun. 30, 2021	Jun. 30, 2021 contract	Dec. 31, 2020 USD ($) securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	$ 333,578,000				$ 174,804,000
Less than 12 months, unrealized loss	5,973,000				$ 1,925,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		81			51
12 months or more, fair value	14,464,000				$ 11,740,000
12 months or more, unrealized loss	435,000				$ 381,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		14			15
Total unrealized loss position, fair value	348,042,000				$ 186,544,000
Total unrealized loss	6,408,000				2,306,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	0
Available-for-sale Securities, Amortized Cost Basis	839,682,000				734,544,000
Gross Unrealized Gains	16,363,000				20,775,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6,408,000				2,306,000
Available-for-sale investment securities, at fair value (amortized cost of $839,682 at June 30, 2021 and $734,544 at December 31, 2020) (a)	849,637,000				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	4,300,000				2,700,000
States and political subdivisions
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	73,895,000				17,651,000
Less than 12 months, unrealized loss	1,713,000				$ 124,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		28			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	73,895,000				$ 17,651,000
Total unrealized loss	1,713,000				124,000
Available-for-sale Securities, Amortized Cost Basis	221,354,000				110,401,000
Gross Unrealized Gains	4,212,000				4,642,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,713,000				124,000
Available-for-sale investment securities, at fair value (amortized cost of $839,682 at June 30, 2021 and $734,544 at December 31, 2020) (a)	223,853,000				114,919,000
Residential mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	228,726,000				156,659,000
Less than 12 months, unrealized loss	3,744,000				$ 1,795,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		45			45
12 months or more, fair value	12,636,000				$ 9,892,000
12 months or more, unrealized loss	263,000				$ 229,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		12			13
Total unrealized loss position, fair value	241,362,000				$ 166,551,000
Total unrealized loss	4,007,000				2,024,000
Available-for-sale Securities, Amortized Cost Basis	571,447,000				609,865,000
Gross Unrealized Gains	11,712,000				15,377,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	4,007,000				2,024,000
Available-for-sale investment securities, at fair value (amortized cost of $839,682 at June 30, 2021 and $734,544 at December 31, 2020) (a)	579,152,000				623,218,000
Commercial mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	20,302,000
Less than 12 months, unrealized loss	321,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		6
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	20,302,000
Total unrealized loss	321,000
Available-for-sale Securities, Amortized Cost Basis	27,840,000				4,622,000
Gross Unrealized Gains	112,000				161,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	321,000				0
Available-for-sale investment securities, at fair value (amortized cost of $839,682 at June 30, 2021 and $734,544 at December 31, 2020) (a)	27,631,000				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	1,828,000				$ 1,848,000
12 months or more, unrealized loss	172,000				$ 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	1,828,000				$ 2,342,000
Total unrealized loss	172,000				158,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities		2
Available-for-sale Securities, Amortized Cost Basis	4,696,000				4,696,000
Gross Unrealized Gains	242,000				192,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	172,000				158,000
Available-for-sale investment securities, at fair value (amortized cost of $839,682 at June 30, 2021 and $734,544 at December 31, 2020) (a)	4,766,000				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	14,345,000				4,960,000
Gross Unrealized Gains	85,000				403,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	195,000				0
Available-for-sale investment securities, at fair value (amortized cost of $839,682 at June 30, 2021 and $734,544 at December 31, 2020) (a)	14,235,000				$ 5,363,000
Agency Securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	10,655,000
Less than 12 months, unrealized loss	195,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		2
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	10,655,000
Total unrealized loss	$ 195,000