Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premises and equipment
Total	$ 296,794	$ 278,761
Less accumulated depreciation	(113,284)	(104,224)
Net premises and equipment	183,510	174,537
Depreciation expense charged to operations	11,500	11,100	$ 11,100
Amortization expense	2,300	1,800	$ 1,700
Land
Premises and equipment
Total	56,454	55,590
Buildings and leasehold improvements
Premises and equipment
Total	$ 148,404	139,946
Buildings and leasehold improvements | Minimum
Premises and equipment
Useful Life	15 years
Buildings and leasehold improvements | Maximum
Premises and equipment
Useful Life	40 years
Equipment and furnishings
Premises and equipment
Total	$ 88,323	79,585
Equipment and furnishings | Minimum
Premises and equipment
Useful Life	3 years
Equipment and furnishings | Maximum
Premises and equipment
Useful Life	10 years
Construction in process
Premises and equipment
Total	$ 3,613	3,640
Computer software
Premises and equipment
Useful Life	36 months
Total	$ 9,700	$ 6,300