Accounting Standards Updates Accounting Standards Updates (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		$ 308,121		$ 308,121		$ 265,007
Noninterest income		$ 18,603	$ 17,202	$ 57,591	$ 51,892
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle						1,780
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle	$ 65					0
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified from AOCI to retained earnings due to Tax Cuts and Jobs Act						$ 10,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Contingent commissions | Insurance Business Segment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Noninterest income	1,800
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 1,800