Business Combinations - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets acquired
Loans	$ 22,419,905		$ 18,210,724
Goodwill	1,078,892		690,637
Deposits
Savings, NOW and money market	$ 11,077,789		$ 9,365,013
USAmeriBancorp, Inc.
Assets acquired
Cash and cash equivalents		$ 156,612
Premises and equipment		62,066
Bank owned life insurance		49,052
Accrued interest receivable		12,123
Goodwill		388,255
Other intangible assets		45,906
Other assets
Deferred taxes		8,698
Other real estate owned		4,073
FHLB and FRB stock		38,809
Tax credit investments		20,138
Other		26,416
Total other assets		98,134
Total assets acquired		5,079,432
Deposits
Non-interest bearing		887,083
Savings, NOW and money market		1,678,115
Time		999,645
Total deposits		3,564,843
Short-term borrowings		649,979
Long-term borrowings		87,283
Junior subordinated debentures issued to capital trusts		13,249
Accrued expenses and other liabilities		26,848
Total liabilities assumed		4,342,202
Common stock issued in acquisition		737,230
Investment securities held to maturity | USAmeriBancorp, Inc.
Assets acquired
Investment securities		214,217
Investment securities available for sale | USAmeriBancorp, Inc.
Assets acquired
Investment securities		308,385
USAmeriBancorp, Inc.
Assets acquired
Loans		$ 3,744,682