Loans and Allowance - Allowance for Credit Losses and Loan Portfolio by Loan Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Allowance Balances:
Individually evaluated for impairment	$ 1,788		$ 888
Collectively evaluated for impairment	71,566		65,149
Total Allowance for Loan Losses	73,354	$ 70,471	66,037	$ 63,456	$ 62,186	$ 62,453
Loan Balance [Abstract]
Individually evaluated for impairment	29,771		30,579
Collectively evaluated for impairment	6,426,838		5,065,844
Loans	6,483,448		5,139,645
Loans Acquired with Deteriorated Credit Quality
Allowance Balances:
Total Allowance for Loan Losses
Loan Balance [Abstract]
Loans	26,839		43,222
Commercial
Allowance Balances:
Individually evaluated for impairment	476		37
Collectively evaluated for impairment	29,207		27,659
Total Allowance for Loan Losses	29,683	28,906	27,696	26,503	26,321	26,478
Loan Balance [Abstract]
Individually evaluated for impairment	6,781		4,762
Collectively evaluated for impairment	1,874,225		1,520,981
Loans	1,882,373		1,532,396
Commercial | Loans Acquired with Deteriorated Credit Quality
Allowance Balances:
Total Allowance for Loan Losses
Loan Balance [Abstract]
Loans	1,367		6,653
Commercial Real Estate
Allowance Balances:
Individually evaluated for impairment	923		553
Collectively evaluated for impairment	25,824		23,108
Total Allowance for Loan Losses	26,747	25,236	23,661	22,937	22,280	22,145
Loan Balance [Abstract]
Individually evaluated for impairment	18,911		21,358
Collectively evaluated for impairment	3,027,247		2,315,686
Loans	3,070,115		2,371,765
Commercial Real Estate | Loans Acquired with Deteriorated Credit Quality
Allowance Balances:
Total Allowance for Loan Losses
Loan Balance [Abstract]
Loans	23,957		34,721
Consumer
Allowance Balances:
Individually evaluated for impairment
Collectively evaluated for impairment	3,591		2,923
Total Allowance for Loan Losses	3,591	3,372	2,923	2,786	2,684	2,689
Loan Balance [Abstract]
Individually evaluated for impairment	6		9
Collectively evaluated for impairment	86,400		77,470
Loans	86,406		77,479
Consumer | Loans Acquired with Deteriorated Credit Quality
Allowance Balances:
Total Allowance for Loan Losses
Loan Balance [Abstract]
Loans
Residential
Allowance Balances:
Individually evaluated for impairment	389		298
Collectively evaluated for impairment	12,942		11,457
Total Allowance for Loan Losses	13,331	12,955	11,755	11,228	10,899	11,139
Loan Balance [Abstract]
Individually evaluated for impairment	4,073		4,450
Collectively evaluated for impairment	1,435,089		1,151,396
Loans	1,440,677		1,157,694
Residential | Loans Acquired with Deteriorated Credit Quality
Allowance Balances:
Total Allowance for Loan Losses
Loan Balance [Abstract]
Loans	1,515		1,848
Lease financing receivables, net of unearned income
Allowance Balances:
Individually evaluated for impairment
Collectively evaluated for impairment	2		2
Total Allowance for Loan Losses	2	$ 2	2	$ 2	$ 2	$ 2
Loan Balance [Abstract]
Individually evaluated for impairment
Collectively evaluated for impairment	3,877		311
Loans	3,877		311
Lease financing receivables, net of unearned income | Loans Acquired with Deteriorated Credit Quality
Allowance Balances:
Total Allowance for Loan Losses
Loan Balance [Abstract]
Loans