Premises and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Premises and equipment before accumulated depreciation	$ 178,851	$ 177,280
Accumulated depreciation	97,546	93,093
Total premises and equipment	81,305	84,187
Rental expense	8,500	7,800	$ 7,900
Future Minimum Rental Payments [Abstract]
2018	7,910
2019	7,227
2020	6,547
2021	5,352
2022	4,646
Thereafter	16,660
Total	48,342
Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment before accumulated depreciation	121,771	121,037
Equipment [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment before accumulated depreciation	$ 57,080	$ 56,243
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Building and Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Building and Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years