Changes in Accumulated Other Comprehensive Income by Component - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated other comprehensive income
Beginning balance	$ 460,305	$ 440,780	$ 399,952
Other comprehensive income (loss) before reclassifications	2,557	2,848	(844)
Losses (gains) reclassified from other comprehensive income	87	(87)	165
Net current period other comprehensive income (loss)	2,644	2,761	(679)
Ending balance	480,461	460,305	440,780
Realized loss	(100)		(200)
Realized gain		100
Changes in other comprehensive (loss) income, tax expense (benefit)	(700)		(100)
Accumulated Other Comprehensive Income, net of taxes
Accumulated other comprehensive income
Beginning balance	2,919	158	837
Ending balance	$ 5,563	$ 2,919	$ 158

Amount of realized gain 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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