Non Purchased Loans - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Restructured loans discontinued past due period	90 days
Allowance for loan losses attributable to restructured loans	$ 49,026,000	$ 46,211,000
Non-Purchased
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonperforming loans charged off past due period	90 days
Number of restructured loans | loan	1	4
Restructured loans discontinued past due period	90 days	90 days
Average recorded investment in impaired loans	$ 27,080,000	$ 21,998,000	$ 23,209,000
Interest income recognized on impaired loans			624,000
Modifications, recorded investment	5,325,000	5,588,000	$ 7,447,000
Modifications, subsequent default, recorded investment		184,000
Remaining availability under commitments to lend additional funds on restructured loans	42,000	18,000
Unfunded commitment	6,982,000	9,333,000
Non-Purchased | Nonaccruing Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Outstanding balance of restructured loans	41,000	649,000
Non-Purchased | Restructured Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Outstanding balance of restructured loans	3,128,000	2,673,000
Allowance for loan losses attributable to restructured loans	$ 34,000	$ 85,000