Goodwill and Identifiable Intangible Assets - Schedule of Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 103,513	$ 101,663
Accumulated Amortization	87,153	80,983
Net Carrying Amount	$ 16,360	20,680
Remaining Weighted-Average Amortization Periods in Years	6 years 3 months 18 days
Core Deposit Intangibles [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 87,674	85,824
Accumulated Amortization	73,494	67,843
Net Carrying Amount	$ 14,180	17,981
Remaining Weighted-Average Amortization Periods in Years	5 years 2 months 12 days
Insurance Intangibles [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 13,824	13,824
Accumulated Amortization	12,026	11,615
Net Carrying Amount	$ 1,798	2,209
Remaining Weighted-Average Amortization Periods in Years	15 years 3 months 18 days
Banking Charters [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,325	1,325
Accumulated Amortization	943	877
Net Carrying Amount	$ 382	448
Remaining Weighted-Average Amortization Periods in Years	5 years 8 months 12 days
Borrower Relationship Intangible [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 690	690
Accumulated Amortization	690	648
Net Carrying Amount	$ 0	$ 42