Loans and Allowance for Loan Losses - Rollforward of Purchase Credit Impaired Loans (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Gross Carrying Value
Gross carrying value, beginning balance	$ 74,324
Year-to-date settlements	(21,332)
Gross carrying value, ending balance	52,992
Accretable Yield
Accretable yield, beginning balance	(132)
Year-to-date settlements	21
Accretable yield, ending balance	(111)
Nonaccretable Yield
Nonaccretable yield, beginning balance	(31,537)
Year-to-date settlements	12,262
Nonaccretable yield, ending balance	(19,275)
Net Carrying Value
Net carrying value, beginning balance	42,655
Year-to-date settlements	(9,049)
Net carrying value, ending balance	$ 33,606