Changes in Accumulated Other Comprehensive Income by Component - Summary (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Accumulated other comprehensive income
Beginning balance	$ 440,780	$ 399,952
Other comprehensive income (loss) before reclassifications	1,419	(1,208)
(Gains) losses reclassified from other comprehensive income	(3)	70
Net current period other comprehensive income (loss)	1,416	(1,138)
Ending balance	442,549	394,344
Losses from the sale of available-for-sale securities	100	(100)
Changes in other comprehensive (loss) income, tax (benefit) expense	(400)	300
Accumulated Other Comprehensive Income, net of taxes
Accumulated other comprehensive income
Beginning balance	158	837
Ending balance	$ 1,574	$ (301)

Amount of realized gain (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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