Acquisition Activity - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Mar. 23, 2018	Jan. 12, 2018	Dec. 31, 2017	Jul. 31, 2017	Dec. 31, 2016
Assets
Non-compete agreement				$ 156
Liabilities
Goodwill	$ 1,223,772				$ 1,188,902		$ 726,856
Gibraltar Private Bank & Trust Company
Assets
Cash and cash equivalents			$ 102,575
Investment securities			19,169
Equity securities			27,519
Loans		$ 1,500,000	1,465,278
Core deposit intangible assets			18,529
Other assets			12,011
Total assets acquired			1,645,081
Liabilities
Deposit liabilities			1,064,803
Long-term borrowings			405,107
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities			5,960
Other liabilities			7,036
Total liabilities assumed			1,482,906
Goodwill	52,500		$ 52,491
Sabadell United
Assets
Cash and cash equivalents						$ 318,819
Investment securities						964,123
Loans						4,030,777
Core deposit intangible assets						66,600
Deferred tax asset, net						44,480
Other assets						92,820
Total assets acquired						5,517,619
Liabilities
Deposit liabilities						4,382,780
Short-term borrowings						520,539
Other liabilities						35,143
Total liabilities assumed						4,938,462
Goodwill	$ 441,000					$ 441,045