Loans and Allowance for Loan Losses - Disaggregated analysis of activity in the allowance for acquired credit impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Allowance for loan losses:
Reduction due to loan removals	$ (142)	$ (180)	$ (245)	$ (886)
Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	1,384	1,829	1,384	1,829
Loans collectively evaluated for impairment	52,206	46,045	52,206	46,045
Loans:
Loans individually evaluated for impairment	54,509	62,593	54,509	62,593
Loans collectively evaluated for impairment	8,566,818	7,134,946	8,566,818	7,134,946
Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	4,514	4,084	4,604	4,627
Provision (benefit) for loan losses	251	522	264	685
Reduction due to loan removals	(142)	(180)	(245)	(886)
Balance at the end of the period	4,623	4,426	4,623	4,426
Loans collectively evaluated for impairment	4,623	4,426	4,623	4,426
Loans:
Loans collectively evaluated for impairment	424,584	556,405	424,584	556,405
Carrying value	424,584	556,405	424,584	556,405	$ 489,723
Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	2,180,281	3,076,424	2,180,281	3,076,424
Carrying value	2,180,281	3,076,424	2,180,281	3,076,424	2,594,826
Residential real estate \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	2,164	2,509	2,246	3,553
Provision (benefit) for loan losses	279	137	295	(807)
Reduction due to loan removals	(97)	(132)	(195)	(232)
Balance at the end of the period	2,346	2,514	2,346	2,514
Loans collectively evaluated for impairment	2,346	2,514	2,346	2,514
Loans:
Loans collectively evaluated for impairment	184,208	229,502	184,208	229,502
Carrying value	184,208	229,502	184,208	229,502	207,482
Commercial non-owner occupied real estate \| Construction and land development \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	715	846	715	846
Loans collectively evaluated for impairment	5,003	5,341	5,003	5,341
Loans:
Loans individually evaluated for impairment	36,130	42,392	36,130	42,392
Loans collectively evaluated for impairment	843,594	864,498	843,594	864,498
Commercial non-owner occupied real estate \| Construction and land development \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	717	215	717	180
Provision (benefit) for loan losses	81	390	81	478
Reduction due to loan removals		(29)		(82)
Balance at the end of the period	798	576	798	576
Loans collectively evaluated for impairment	798	576	798	576
Loans:
Loans collectively evaluated for impairment	27,014	40,951	27,014	40,951
Carrying value	27,014	40,951	27,014	40,951	32,942
Commercial non-owner occupied real estate \| Construction and land development \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	60,391	281,282	60,391	281,282
Carrying value	60,391	281,282	60,391	281,282	165,070
Commercial non-owner occupied real estate \| Other commercial non-owner occupied real estate \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	1	93	1	93
Loans collectively evaluated for impairment	10,310	7,116	10,310	7,116
Loans:
Loans individually evaluated for impairment	101	1,348	101	1,348
Loans collectively evaluated for impairment	1,723,539	1,133,887	1,723,539	1,133,887
Commercial non-owner occupied real estate \| Other commercial non-owner occupied real estate \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	847	261	801	288
Provision (benefit) for loan losses	162	375	213	361
Reduction due to loan removals			(5)	(13)
Balance at the end of the period	1,009	636	1,009	636
Loans collectively evaluated for impairment	1,009	636	1,009	636
Loans:
Loans collectively evaluated for impairment	164,540	227,739	164,540	227,739
Carrying value	164,540	227,739	164,540	227,739	196,764
Commercial non-owner occupied real estate \| Other commercial non-owner occupied real estate \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	595,367	752,465	595,367	752,465
Carrying value	595,367	752,465	595,367	752,465	679,253
Consumer loans \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	707	594	761	461
Provision (benefit) for loan losses	(237)	(19)	(291)	114
Reduction due to loan removals		(3)		(3)
Balance at the end of the period	470	572	470	572
Loans collectively evaluated for impairment	470	572	470	572
Loans:
Loans collectively evaluated for impairment	38,624	45,633	38,624	45,633
Carrying value	38,624	45,633	38,624	45,633
Consumer loans \| Acquired non-credit impaired loans
Loans:
Carrying value	885,751	1,082,167	885,751	1,082,167	983,015
Consumer loans \| Home equity loans \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	125	180	125	180
Loans collectively evaluated for impairment	3,052	3,188	3,052	3,188
Loans:
Loans individually evaluated for impairment	2,436	3,144	2,436	3,144
Loans collectively evaluated for impairment	511,806	453,802	511,806	453,802
Consumer loans \| Home equity loans \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	208,777	278,906	208,777	278,906
Carrying value	208,777	278,906	208,777	278,906	242,425
Commercial and industrial \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	394	485	394	485
Loans collectively evaluated for impairment	7,101	6,226	7,101	6,226
Loans:
Loans individually evaluated for impairment	2,674	1,834	2,674	1,834
Loans collectively evaluated for impairment	1,111,839	939,233	1,111,839	939,233
Commercial and industrial \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	79	505	79	145
Provision (benefit) for loan losses	(34)	(361)	(34)	539
Reduction due to loan removals	(45)	(16)	(45)	(556)
Balance at the end of the period		128		128
Loans collectively evaluated for impairment		128		128
Loans:
Loans collectively evaluated for impairment	10,198	12,580	10,198	12,580
Carrying value	10,198	12,580	10,198	12,580
Commercial and industrial \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	151,579	304,864	151,579	304,864
Carrying value	151,579	304,864	151,579	304,864	212,537
Other income producing property \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	78	144	78	144
Loans collectively evaluated for impairment	1,281	1,269	1,281	1,269
Loans:
Loans individually evaluated for impairment	2,064	3,240	2,064	3,240
Loans collectively evaluated for impairment	212,139	202,267	212,139	202,267
Other income producing property \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	111,006	169,392	111,006	169,392
Carrying value	111,006	169,392	111,006	169,392	133,110
Consumer \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	3	7	3	7
Loans collectively evaluated for impairment	3,569	3,064	3,569	3,064
Loans:
Loans individually evaluated for impairment	98	257	98	257
Loans collectively evaluated for impairment	503,370	416,393	503,370	416,393
Consumer \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	99,690	126,665	99,690	126,665
Commercial loans \| Acquired non-credit impaired loans
Loans:
Carrying value	$ 1,294,530	$ 1,994,257	$ 1,294,530	$ 1,994,257	$ 1,611,811

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The sum of the periodic provision charged to earnings before adjustment for amounts covered under loss sharing agreement.

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Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount of increase (decrease) in allowance for credit loss on financing receivable.

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