Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Acquired thrift's tax bad debt reserve	$ 2,500		$ 2,500	$ 2,500	$ 2,500
Deferred tax assets, net	64,736		64,736	100,207
Unrecognized tax benefit that would affect effective tax rate	12,900		12,900	1,400	$ 936,000
Standard Bancshares and NI Bancshares Acquisitions
Income Taxes [Line Items]
Deferred tax assets, net	41,500		41,500
NI Bancshares and Peoples Bank Acquisitions
Income Taxes [Line Items]
Deferred tax assets, net				$ 4,400
Federal
Income Taxes [Line Items]
Revaluation of deferred tax assets	$ (26,600)		(26,600)
State and Local Jurisdiction
Income Taxes [Line Items]
Revaluation of deferred tax assets		$ 2,800	$ 2,800