Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reconciliation of Federal Statutory to Actual Tax Expense:
Federal statutory income tax at 21% for 2018 and 35% for 2017	$ 9,995	$ 10,970	$ 19,086	$ 21,596
Tax-exempt interest income	(2,045)	(2,632)	(4,060)	(5,181)
Share-based compensation	(91)	(29)	(532)	(784)
Tax-exempt earnings and gains on life insurance	(211)	(1,040)	(458)	(1,354)
Tax credits	(62)	(82)	(23)	(188)
Other	375	20	559	286
Actual Tax Expense	$ 7,961	$ 7,207	$ 14,572	$ 14,375
Federal statutory income tax rate	21.00%	35.00%	21.00%	35.00%
Effective Tax Rate	16.70%	23.00%	16.00%	23.30%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other deductions.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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