Accumulated Other Comprehensive Loss Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on sale of investment securities									$ 4,476	$ 3,513	$ 2,130
Income tax expense	$ 14,972	$ 7,003	$ 6,812	$ 7,647	$ 6,338	$ 6,577	$ 6,303	$ 5,866	36,435	25,083	28,414
Net Income Available to Common Shareholders	$ 9,669	$ 13,932	$ 14,685	$ 16,026	$ 14,656	$ 13,232	$ 12,541	$ 11,702	54,310	52,128	54,097
Unrealized Gains (Losses) on Securities Available-for-Sale | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on sale of investment securities									4,476	3,513	2,130
Income tax expense									1,657	1,297	786
Net Income Available to Common Shareholders									$ 2,819	$ 2,216	$ 1,344