Goodwill and other Intangible Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill [Roll Forward]
Beginning Balance	$ 264,997,000	$ 152,373,000
Goodwill acquired	(1,363,000)	112,624,000
Ending Balance	263,634,000	264,997,000	152,373,000
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	47,717,000	47,910,000
Less: accumulated amortization	27,400,000	22,353,000
Net carrying amount	20,317,000	25,557,000
Amortization Expense [Abstract]
Amortization of intangible assets	5,047,000	4,872,000	3,394,000
Future Amortization Expense [Abstract]
2015	4,800,000
2016	3,300,000
2017	2,800,000
2018	2,200,000
2019	1,700,000
Thereafter	3,700,000
Indefinite-lived intangible assets (Excluding goodwill)	1,800,000
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	12 years
Core Deposits Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	19,401,000	19,401,000
Less: accumulated amortization	12,522,000	10,083,000
Net carrying amount	6,879,000	9,318,000
Identified Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,316,000	28,509,000
Less: accumulated amortization	14,878,000	12,270,000
Net carrying amount	$ 13,438,000	$ 16,239,000