Acquisition Activity - Consideration (Details) - USD ($) $ in Thousands		9 Months Ended
	Jul. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Total equity consideration		$ 211,043	$ 0
Goodwill		$ 1,158,683		$ 726,856	$ 724,603
Sabadell United
Business Acquisition [Line Items]
Total equity consideration	$ 211,043
Cash	809,159
Total consideration paid	1,020,202
Fair value of net assets assumed including identifiable intangible assets	588,375
Goodwill	$ 431,827
Sabadell United | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares)	2,610,304
Common stock issued	$ 211,043