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Securities, Available for Sale (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt securities, available-for-sale [Abstract]
Amortized cost	$ 1,380,352		$ 1,318,711
Unrealized gains	23,958		32,166
Unrealized losses	17,282		2,179
Estimated fair value	1,387,028		1,348,698
Allowance for credit losses on AFS securities	0		0
Gross realized gains	0	$ 3
Gross realized losses	0
Gains from calls on securities available for sale		$ 3
Federal Agency [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	258,479		245,590
Unrealized gains	2		59
Unrealized losses	9,594		2,052
Estimated fair value	248,887		243,597
State & Municipal [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	49,048		42,550
Unrealized gains	128		630
Unrealized losses	1,151		0
Estimated fair value	48,025		43,180
Mortgage-Backed, Government Sponsored Enterprises [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	606,988		521,448
Unrealized gains	12,506		17,079
Unrealized losses	5,448		22
Estimated fair value	614,046		538,505
Mortgage-Backed, U.S. Government Agency Securities [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	57,913		55,049
Unrealized gains	1,390		2,332
Unrealized losses	110		47
Estimated fair value	59,193		57,334
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	278,532		311,710
Unrealized gains	6,568		7,549
Unrealized losses	934		58
Estimated fair value	284,166		319,201
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	101,892		114,864
Unrealized gains	2,655		3,739
Unrealized losses	0		0
Estimated fair value	104,547		118,603
Corporate [Member]
Debt securities, available-for-sale [Abstract]
Amortized cost	27,500		27,500
Unrealized gains	709		778
Unrealized losses	45		0
Estimated fair value	$ 28,164		$ 28,278

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) 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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