Changes in Accumulated Other Comprehensive Income by Component - Reclassification Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax (expense) benefit	$ (2,581)			$ (9,488)			$ (16,378)	$ (23,391)
Net income	9,540	$ 9,565	$ 24,653	27,644	$ 23,101	$ 20,190	43,758	70,935
Realized Gains (Losses) on Sale of Available-for-sale Securities | Amounts Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) from the sale of available-for-sale securities	(7)			(7)			221	(94)
Tax (expense) benefit	5			2			(60)	23
Net income	$ (2)			$ (5)			$ 161	$ (71)