Purchased Credit Impaired Loans - Accretable Yield or Income Expected to be Collected (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	$ 2,423	$ 2,607	$ 2,890	$ 3,951
Additions		941		1,608
Accretion	(1,004)	(686)	(2,441)	(5,082)
Reclassification from nonaccretable	798	449	1,768	3,501
Disposals	(16)		(16)	(667)
Ending balance	2,201	$ 3,311	2,201	$ 3,311
Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, carrying amount	$ 20,600		$ 20,600		$ 25,300