Summary of Net Assets Acquired (at Fair Value) and Consideration Transferred (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	May 31, 2015	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Total assets acquired				$ 1,321,322
Total liabilities assumed				$ 1,160,044
Goodwill acquired		$ 228,396	$ 228,346		$ 209,758
Marquette [Member]
Business Acquisition [Line Items]
Loans	$ 980,404
Investment securities	177,694
Cash and due from banks	95,351
Premises and equipment, net	11,508
Identifiable intangible assets	14,881
Other assets	32,336
Total assets acquired	1,312,174
Noninterest-bearing deposits	226,161
Interest-bearing deposits	708,675
Short-term debt	112,133
Long-term debt	89,971
Other liabilities	14,135
Total liabilities assumed	1,151,075
Net identifiable assets acquired	161,099
Goodwill acquired	18,638
Net assets acquired	$ 179,737
Company's common shares issued	3,470
Purchase price per share of the Company's common stock	$ 51.79
Fair value of total consideration transferred	$ 179,737