Subsequent Events (Details) - Narrative - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jan. 06, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Acquisition and integration related expenses		$ 14,352	$ 1,389	$ 13,872
Standard Bancshares, Inc.
Subsequent Event [Line Items]
Acquisition and integration related expenses		$ 8,000
Standard Bancshares, Inc. | Subsequent Event
Subsequent Event [Line Items]
Fixed exchange ratio (in shares)	0.4350
Consideration transferred	$ 580,483
Common stock, shares issued (in shares)	21,057,085
Cash paid	$ 47,125
First Midwest Bancorp, Inc. | Subsequent Event
Subsequent Event [Line Items]
Share price (in dollars per share)	$ 25.34
Standard Bancshares, Inc. | Subsequent Event
Subsequent Event [Line Items]
Share price (in dollars per share)	$ 11.02
Forecast | Standard Bancshares, Inc.
Subsequent Event [Line Items]
Acquisition and integration related expenses	$ 27,000