Goodwill and Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning balance	$ 265,439	$ 265,957
Goodwill acquired	2,604	2,047
Goodwill adjustments		(2,565)
Ending balance	268,043	265,439	$ 265,957
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	42,607	41,313
Less: accumulated amortization	29,187	25,498
Net carrying amount	13,420	15,815
Impairment of intangible assets	1,500	0
Impairment of goodwill	0	2,565
Amortization Expense [Abstract]
Amortization of intangible assets	3,960	3,928	$ 4,864
Future Amortization Expense [Abstract]
2018	3,300
2019	2,700
2020	2,200
2021	1,600
2022	1,100
Thereafter	$ 2,500
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life	1 year
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life	20 years
Core Deposits Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 8,975	8,975
Less: accumulated amortization	6,581	5,626
Net carrying amount	2,394	3,349
Identified Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	33,632	32,338
Less: accumulated amortization	22,606	19,872
Net carrying amount	$ 11,026	$ 12,466