Securities (Summary of Investments) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale debt securities amortized cost basis	$ 896,435,000	$ 895,273,000
Available for sale debt securities unrealized gains	26,097,000	9,117,000
Available for sale debt securities unrealized losses	(5,140,000)	(4,900,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	917,392,000	899,490,000
Total securities amortized cost	896,435,000	895,273,000
Total securities unrealized gains	26,097,000	9,117,000
Total securities unrealized losses	(5,140,000)	(4,900,000)
Total securities fair value	917,392,000	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	132,262,000	157,255,000
Available for sale debt securities unrealized gains	1,408,000	626,000
Available for sale debt securities unrealized losses	(169,000)	(233,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	133,501,000	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	739,701,000	713,553,000
Available for sale debt securities unrealized gains	24,689,000	8,491,000
Available for sale debt securities unrealized losses	(46,000)	(2,964,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	764,344,000	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	13,328,000	13,324,000
Available for sale debt securities unrealized gains	0	0
Available for sale debt securities unrealized losses	(2,232,000)	(745,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	11,096,000	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	11,144,000	11,141,000
Available for sale debt securities unrealized gains	0	0
Available for sale debt securities unrealized losses	(2,693,000)	(958,000)
Available for sale debt securities allowance for credit losses	0
Available for sale debt securities, at fair value	$ 8,451,000	$ 10,183,000

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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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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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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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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-Publisher FASB
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This represents the total available for sale and held to maturity securities unrealized gains.

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

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