Amortized cost of 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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Amount of 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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Amount of restricted 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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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

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The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

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Investment Securities Narrative (Details)	9 Months Ended
Investment Securities Narrative (Details)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Security	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Investments [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 11,510,000	$ 990,000	$ 990,000	$ 11,510,000	$ 11,510,000	$ 11,510,000
Other-than-temporary Impairment Loss, Debt Securities, Portion Recognized in Earnings	$ 0
Number of Held to Maturity investments in unrealized loss position \| Security		0
Amortized cost		$ 2,274,913,000
Available-for-sale Securities, Fair Value Disclosure		2,315,541,000		2,080,294,000
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized cost		183,696,000
Available-for-sale Securities, Fair Value Disclosure		183,785,000
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized cost		530,448,000
Available-for-sale Securities, Fair Value Disclosure		547,344,000
Collateral Pledged [Member]
Schedule of Investments [Line Items]
Securities pledged as collateral		$ 391,500,000		$ 973,400,000