Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Gross Carrying Value [Abstract]
Goodwill not subject to amortization	$ 109,037		$ 109,037	$ 63,910
Intangibles from branch acquisition	3,015		3,015	3,015
Core deposit intangibles	32,355		32,355	19,862
Customer list intangibles	16,029		16,029	3,731
Total Goodwill and Intangible Assets, Gross Carrying Value	160,436		160,436	90,518
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Goodwill not subject to amortization (effective 1/1/02), Accumulated Amortization	3,760		3,760	3,760
Total Goodwill and Intangible Assets, Accumulated Amortization	23,440		23,440	20,533
Total Amortization Expense [Abstract]
Amortization of intangible assets			3,215	2,153	$ 1,909
Estimated amortization expense [Abstract]
For year ended 12/31/19	5,355		5,355
For year ended 12/31/20	4,644		4,644
For year ended 12/31/21	3,996		3,996
For year ended 12/31/22	3,630		3,630
For year ended 12/31/23	3,318		3,318
Goodwill, Acquired During Period	18,636
First BancTrust [Member]
Estimated amortization expense [Abstract]
Goodwill, Acquired During Period		$ 26,491	26,500
Intangibles from branch acquisitions
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization	3,015		3,015	3,015
Core deposit intangibles
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization	14,017		14,017	11,473
Total Amortization Expense [Abstract]
Amortization of intangible assets			2,544	1,829	1,628
Customer list intangibles
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization	$ 2,648		2,648	2,285
Total Amortization Expense [Abstract]
Amortization of intangible assets			363	183	183
Mortgage Servicing Rights [Member]
Total Amortization Expense [Abstract]
Amortization of intangible assets			$ 308	$ 141	$ 98