Changes in Accumulated Other Comprehensive Income by Component - Reclassification Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax expense (benefit)									$ (20,515)	$ (16,386)	$ (44,739)
Net income	$ 18,895	$ 18,344	$ 18,186	$ 9,156	$ 31,552	$ 26,086	$ 25,814	$ 72	64,581	83,524	88,226
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									(111)	197	11
Tax expense (benefit)									24	(32)	(4)
Net income									$ (87)	$ 165	$ 7