Purchased Credit Impaired ("PCI") Loans - Rollforward of PCI Loans, Net of Allowance for Loan Losses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 69,741	$ 33,925
Acquisitions		49,155
Principal reductions and interest payments	(38,165)	(16,319)
Accretion of loan discount	5,118	5,473
Changes in contractual and expected cash flows due to remeasurement	10,101	8,036
Reductions due to disposals		(3,186)
Balance at end of period	46,795	77,084
Contractual Cashflows
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	112,710	66,003
Acquisitions		68,763
Principal reductions and interest payments	(38,165)	(16,319)
Accretion of loan discount	0	0
Changes in contractual and expected cash flows due to remeasurement	4,341	11,110
Reductions due to disposals		(6,393)
Balance at end of period	78,886	123,164
Non-accretable Difference
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	29,005	18,902
Acquisitions		14,296
Principal reductions and interest payments	0	0
Accretion of loan discount	0	0
Changes in contractual and expected cash flows due to remeasurement	(8,939)	(702)
Reductions due to disposals		(1,612)
Balance at end of period	20,066	30,884
Accretable Yield
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	13,964	13,176
Acquisitions		5,312
Principal reductions and interest payments	0	0
Accretion of loan discount	5,118	5,473
Changes in contractual and expected cash flows due to remeasurement	3,179	3,776
Reductions due to disposals		(1,595)
Balance at end of period	$ 12,025	$ 15,196