Income Taxes (Detail) - Deferred Tax Assets And Liabilities - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Allowance for credit losses	$ 26,131	$ 26,078
Unrealized losses on securities	18,328	18,527
Alternative minimum tax (AMT) and other credit carryforwards	17,739	29,007
State net operating loss (NOL) carryforwards	7,679	11,917
Equity based compensation	5,469	6,875
Non-equity based compensation	3,739	3,477
Property valuation adjustments	3,003	0
OREO	2,597	3,480
Other	8,693	7,754
Total deferred tax assets	93,378	107,115
Deferred tax liabilities:
Acquisition adjustments	(10,097)	(10,960)
Accrued retirement benefits	(6,065)	(6,447)
Cancellation of indebtedness income	(3,204)	(4,272)
Deferred loan fees and costs	(2,432)	0
Other	(4,631)	(5,045)
Total deferred tax liabilities	(26,429)	(26,724)
Deferred tax valuation allowance	0	0
Net deferred tax assets	66,949	80,391
Tax effect of adjustments related to other comprehensive (loss) income	19,744	11,294
Net deferred tax assets including adjustments	86,693	91,685
Alternative minimum tax credits
Net operating loss carryforwards available to offset future taxable income:
Alternative minimum tax credits	17,739	25,739
Other credits, begin to expire in 2028
Net operating loss carryforwards available to offset future taxable income:
Other credits, begin to expire in 2028	0	3,268
Internal Revenue Service (IRS)
Net operating loss carryforwards available to offset future taxable income:
Gross NOL Carryforwards	922	0
Illinois
Net operating loss carryforwards available to offset future taxable income:
Gross NOL Carryforwards	160,016	232,834
Indiana
Net operating loss carryforwards available to offset future taxable income:
Gross NOL Carryforwards	$ 11,796	$ 17,192