Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income Net Of Tax [Abstract]
Unrealized holding gains (losses) on available-for-sale securities during the period, pre-tax		$ (4,929)	$ (679)	$ (14,057)	$ 5,642
Reclassification adjustment for (gains) losses included in net income, pre-tax	[1]	27	0	24	1
Net other comprehensive income (loss), pre-tax		(4,902)	(679)	(14,033)	5,643
Unrealized holding gains (losses) on available-for-sale securities during the period, tax		1,036	239	2,940	(1,975)
Reclassification adjustment for (gains) losses included in net income, tax	[1]	(6)	0	(5)	(1)
Net other comprehensive income (loss), tax		1,030	239	2,935	(1,976)
Unrealized holding gains (losses) on available-for-sale securities during the period, after tax		(3,893)	(440)	(11,117)	3,667
Reclassification adjustment for (gains) losses included in net income, after-tax	[1]	21	0	19	0
Other comprehensive income (loss), net of tax		$ (3,872)	$ (440)	$ (11,098)	$ 3,667

[1] Pre-tax reclassification adjustments relating to available-for-sale securities are reported in security gains and the tax impact is included in income tax expense on the consolidated statements of income.