Acquisitions (Details) - Acquisition Activity - USD ($) $ / shares in Units, $ in Thousands	Jan. 06, 2017	Mar. 08, 2016	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets
Goodwill			$ 691,527	$ 691,572	$ 340,879	$ 341,513	$ 339,768	$ 319,007
Liabilities
Intangible liabilities			$ 7,503
Standard Bancshares, Inc.
Assets
Cash and due from banks and interest-bearing deposits in other banks	$ 102,149
Securities available-for-sale	214,107
Securities held-to-maturity	0
FHLB and FRB stock	3,247
Loans	1,769,655
OREO	8,424
Investment in BOLI	55,629
Goodwill	339,253
Other intangible assets	31,072
Premises, furniture, and equipment	60,207
Accrued interest receivable and other assets	56,036
Total assets	2,639,779
Liabilities
Noninterest-bearing deposits	675,354
Interest-bearing deposits	1,348,520
Total deposits	2,023,874
Borrowed funds	0
Intangible liabilities	0
Accrued interest payable and other liabilities	35,190
Total liabilities	2,059,064
Consideration Paid
Common stock (2017 - 21,057,085 shares issued at $25.34 per share, 2016 - 3,042,494 shares issued at $18.059 per share), net of issuance costs	533,590
Cash paid	47,125
Total consideration paid	$ 580,715
Common stock, shares issued (in Shares)	21,057,085
Shares issued (in dollars per share)	$ 25.34
NI Bancshares Corporation
Assets
Cash and due from banks and interest-bearing deposits in other banks		$ 72,533
Securities available-for-sale		125,843
Securities held-to-maturity		1,864
FHLB and FRB stock		1,549
Loans		396,181
OREO		2,863
Investment in BOLI		8,384
Goodwill		22,174
Other intangible assets		10,408
Premises, furniture, and equipment		19,636
Accrued interest receivable and other assets		16,453
Total assets		677,888
Liabilities
Noninterest-bearing deposits		130,909
Interest-bearing deposits		464,012
Total deposits		594,921
Borrowed funds		2,416
Intangible liabilities		230
Accrued interest payable and other liabilities		10,239
Total liabilities		607,806
Consideration Paid
Common stock (2017 - 21,057,085 shares issued at $25.34 per share, 2016 - 3,042,494 shares issued at $18.059 per share), net of issuance costs		54,896
Cash paid		15,186
Total consideration paid		$ 70,082
Common stock, shares issued (in Shares)		3,042,494
Shares issued (in dollars per share)		$ 18.059