Business Combinations - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets acquired:
Loans	$ 23,966,327		$ 18,210,724
Goodwill	1,085,710		690,637
Deposits:
Savings, NOW and money market	$ 11,036,700		$ 9,365,013
USAmeriBancorp, Inc.
Assets acquired:
Cash and cash equivalents		$ 156,612
Loans		3,735,162
Premises and equipment		62,066
Bank owned life insurance		49,052
Accrued interest receivable		12,123
Goodwill		395,073
Other intangible assets		45,906
Other assets:
Deferred taxes		11,400
Other real estate owned		4,073
FHLB and FRB stock		38,809
Tax credit investments		20,138
Other		26,416
Total other assets		100,836
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