Acquisition Activity - Consideration (Details) - USD ($) $ in Thousands				6 Months Ended
	Mar. 31, 2018	Mar. 23, 2018	Jul. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Total equity consideration				$ 214,659	$ 0
Goodwill				1,223,772		$ 1,188,902	$ 726,856
Gibraltar Private Bank & Trust Company
Business Acquisition [Line Items]
Total equity consideration		$ 214,659
Cash	$ 214,700	7
Total consideration paid		214,666
Fair value of net assets assumed including identifiable intangible assets		162,175
Goodwill		$ 52,491		52,500
Gibraltar Private Bank & Trust Company | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares)		2,787,773
Common stock issued		$ 214,659
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			579,157
Goodwill			$ 441,045	$ 441,000
Sabadell United | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares)			2,610,304
Common stock issued			$ 211,043