Goodwill and Other Intangible Assets - (Details)	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill [Roll Forward]
Balance at January 1, 2017	$ 470,534,000
Addition to goodwill from acquisition	0
Adjustment to previously recorded goodwill	0
Balance at June 30, 2017	470,534,000
Adjustments to goodwill	0
Community Banks
Goodwill [Roll Forward]
Balance at January 1, 2017	467,767,000
Addition to goodwill from acquisition	0
Adjustment to previously recorded goodwill	0
Balance at June 30, 2017	467,767,000
Insurance
Goodwill [Roll Forward]
Balance at January 1, 2017	2,767,000
Addition to goodwill from acquisition	0
Adjustment to previously recorded goodwill	0
Balance at June 30, 2017	$ 2,767,000