Goodwill and Identifiable Intangible Assets - Goodwill by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 366,156	$ 366,156
Adjustment during 2016		0
Balance, end of period	379,627	366,156
Goodwill from Reliance merger during 2017	13,471
General Banking [Member]
Goodwill [Roll Forward]
Goodwill, beginning of period	321,132	321,132
Adjustment during 2016		0
Balance, end of period	334,603	321,132
Goodwill from Reliance merger during 2017	13,471
Insurance [Member]
Goodwill [Roll Forward]
Goodwill, beginning of period	45,024	45,024
Adjustment during 2016		0
Balance, end of period	45,024	$ 45,024
Goodwill from Reliance merger during 2017	$ 0