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	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Allowance for loan losses:
Reduction due to loan removals	$ (91)	$ (174)	$ (336)	$ (1,060)
Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	1,221	1,657	1,221	1,657
Loans collectively evaluated for impairment	53,716	48,212	53,716	48,212
Loans:
Loans individually evaluated for impairment	54,867	54,640	54,867	54,640
Loans collectively evaluated for impairment	8,873,645	7,551,838	8,873,645	7,551,838
Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	4,623	4,426	4,604	4,627
Provision (benefit) for loan losses	786	(284)	1,050	401
Reduction due to loan removals	(91)	(174)	(336)	(1,060)
Balance at the end of the period	5,318	3,968	5,318	3,968
Loans collectively evaluated for impairment	5,318	3,968	5,318	3,968
Loans:
Loans collectively evaluated for impairment	396,032	516,601	396,032	516,601
Carrying value	396,032	516,601	396,032	516,601	$ 489,723
Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	1,965,603	2,786,102	1,965,603	2,786,102
Carrying value	1,965,603	2,786,102	1,965,603	2,786,102	2,594,826
Residential real estate \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	2,346	2,514	2,246	3,553
Provision (benefit) for loan losses	447	(87)	742	(894)
Reduction due to loan removals	(91)	(116)	(286)	(348)
Balance at the end of the period	2,702	2,311	2,702	2,311
Loans collectively evaluated for impairment	2,702	2,311	2,702	2,311
Loans:
Loans collectively evaluated for impairment	175,044	218,019	175,044	218,019
Carrying value	175,044	218,019	175,044	218,019	207,482
Commercial non-owner occupied real estate \| Construction and land development \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	587	723	587	723
Loans collectively evaluated for impairment	5,429	5,290	5,429	5,290
Loans:
Loans individually evaluated for impairment	32,673	35,776	32,673	35,776
Loans collectively evaluated for impairment	922,645	867,060	922,645	867,060
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	798	576	717	180
Provision (benefit) for loan losses	(38)	(205)	43	273
Reduction due to loan removals		(31)		(113)
Balance at the end of the period	760	340	760	340
Loans collectively evaluated for impairment	760	340	760	340
Loans:
Loans collectively evaluated for impairment	26,930	34,312	26,930	34,312
Carrying value	26,930	34,312	26,930	34,312	32,942
Commercial non-owner occupied real estate \| Construction and land development \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	53,302	222,562	53,302	222,562
Carrying value	53,302	222,562	53,302	222,562	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		81		81
Loans collectively evaluated for impairment	10,551	7,904	10,551	7,904
Loans:
Loans individually evaluated for impairment	87	1,315	87	1,315
Loans collectively evaluated for impairment	1,777,240	1,278,013	1,777,240	1,278,013
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	1,009	636	801	288
Provision (benefit) for loan losses	386	62	599	423
Reduction due to loan removals		(6)	(5)	(19)
Balance at the end of the period	1,395	692	1,395	692
Loans collectively evaluated for impairment	1,395	692	1,395	692
Loans:
Loans collectively evaluated for impairment	149,134	209,518	149,134	209,518
Carrying value	149,134	209,518	149,134	209,518	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	503,443	684,793	503,443	684,793
Carrying value	503,443	684,793	503,443	684,793	679,253
Consumer loans \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	470	572	761	461
Provision (benefit) for loan losses	(9)	(26)	(300)	88
Reduction due to loan removals				(3)
Balance at the end of the period	461	546	461	546
Loans collectively evaluated for impairment	461	546	461	546
Loans:
Loans collectively evaluated for impairment	36,812	44,081	36,812	44,081
Carrying value	36,812	44,081	36,812	44,081
Consumer loans \| Acquired non-credit impaired loans
Loans:
Carrying value	834,633	1,024,651	834,633	1,024,651	983,015
Consumer loans \| Home equity loans \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	121	171	121	171
Loans collectively evaluated for impairment	3,070	3,270	3,070	3,270
Loans:
Loans individually evaluated for impairment	2,345	3,026	2,345	3,026
Loans collectively evaluated for impairment	519,399	470,355	519,399	470,355
Consumer loans \| Home equity loans \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	198,112	259,558	198,112	259,558
Carrying value	198,112	259,558	198,112	259,558	242,425
Commercial and industrial \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	387	475	387	475
Loans collectively evaluated for impairment	7,174	6,448	7,174	6,448
Loans:
Loans individually evaluated for impairment	5,313	1,409	5,313	1,409
Loans collectively evaluated for impairment	1,125,534	990,433	1,125,534	990,433
Commercial and industrial \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period		128	79	145
Provision (benefit) for loan losses		(28)	(34)	511
Reduction due to loan removals		(21)	(45)	(577)
Balance at the end of the period		79		79
Loans collectively evaluated for impairment		79		79
Loans:
Loans collectively evaluated for impairment	8,112	10,671	8,112	10,671
Carrying value	8,112	10,671	8,112	10,671	10,043
Commercial and industrial \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	126,092	247,922	126,092	247,922
Carrying value	126,092	247,922	126,092	247,922	212,537
Other income producing property \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	58	133	58	133
Loans collectively evaluated for impairment	1,301	1,277	1,301	1,277
Loans:
Loans individually evaluated for impairment	2,096	2,930	2,096	2,930
Loans collectively evaluated for impairment	218,861	207,053	218,861	207,053
Other income producing property \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	103,093	150,371	103,093	150,371
Carrying value	103,093	150,371	103,093	150,371	133,110
Consumer \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	2	6	2	6
Loans collectively evaluated for impairment	3,741	3,177	3,741	3,177
Loans:
Loans individually evaluated for impairment	91	213	91	213
Loans collectively evaluated for impairment	524,949	438,576	524,949	438,576
Consumer \| Acquired credit impaired loans
Loans:
Carrying value	36,812	44,081	36,812	44,081	42,492
Consumer \| Acquired non-credit impaired loans
Loans:
Loans collectively evaluated for impairment	93,089	118,029	93,089	118,029
Commercial loans \| Acquired non-credit impaired loans
Loans:
Carrying value	$ 1,130,970	$ 1,761,451	$ 1,130,970	$ 1,761,451	$ 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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