Securities (Summary of Investments) (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale debt securities amortized cost basis	$ 899,839,000	$ 895,273,000
Available for sale debt securities unrealized gains	17,297,000	9,117,000
Available for sale debt securities unrealized losses	(3,286,000)	(4,900,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	913,850,000	899,490,000
Obligations of U.S. government-sponsored enterprises [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale debt securities amortized cost basis	145,778,000	157,255,000
Available for sale debt securities unrealized gains	1,058,000	626,000
Available for sale debt securities unrealized losses	(296,000)	(233,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	146,540,000	157,648,000
Mortgage-backed securities issued by U.S. government-sponsored agencies and U.S. government-sponsored enterprises [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale debt securities amortized cost basis	729,575,000	713,553,000
Available for sale debt securities unrealized gains	16,239,000	8,491,000
Available for sale debt securities unrealized losses	(743,000)	(2,964,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	745,071,000	719,080,000
Individual name issuer trust preferred debt securities
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale debt securities amortized cost basis	13,336,000	13,324,000
Available for sale debt securities unrealized gains	0	0
Available for sale debt securities unrealized losses	(973,000)	(745,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	12,363,000	12,579,000
Corporate bonds [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale debt securities amortized cost basis	11,150,000	11,141,000
Available for sale debt securities unrealized gains	0	0
Available for sale debt securities unrealized losses	(1,274,000)	(958,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	$ 9,876,000	$ 10,183,000

Line items for schedule of Available for Sale and Held to Maturty Securities.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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