Business Combinations (Details) $ / shares in Units, $ in Thousands	Sep. 30, 2017 USD ($)	Jul. 26, 2017 USD ($) office $ / shares	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Assets	$ 23,780,661		$ 22,864,439
Net loans	18,082,496		17,121,684
Deposits	$ 17,312,766		$ 17,730,708
USAmeriBancorp, Inc. Merger
Business Acquisition [Line Items]
Share ratio of common stock issued to USAB shareholders		6.1
Transaction fair value		$ 816,000
USAmeriBancorp, Inc. Merger | Minimum
Business Acquisition [Line Items]
Average stock price (in dollars per share) | $ / shares		$ 11.50
Walkaway rights, average share price (in dollars per share) | $ / shares		11.00
USAmeriBancorp, Inc. Merger | Maximum
Business Acquisition [Line Items]
Average stock price (in dollars per share) | $ / shares		13.00
Walkaway rights, average share price (in dollars per share) | $ / shares		$ 13.50
USAmeriBancorp, Inc.
Business Acquisition [Line Items]
Assets		$ 4,500,000
Net loans		3,600,000
Deposits		$ 3,600,000
Number of offices | office		30