Net Carrying Value of Core Deposit Intangibles (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Core Deposit Intangibles and Aggregate Amortization Expense
Net carrying value	$ 10,900,000	$ 9,512,000
Aggregate amortization expense	2,811,000	2,401,000	2,110,000
Core Deposits Intangibles
Net Core Deposit Intangibles and Aggregate Amortization Expense
Gross carrying value	32,056,000	27,857,000	22,404,000
Accumulated amortization	(21,156,000)	(18,345,000)	(16,230,000)
Net carrying value	10,900,000	9,512,000	6,174,000
Aggregate amortization expense	2,811,000	2,401,000	2,110,000
Estimated Amortization Expense
For the year ending December 31, 2015	2,676,000
For the year ending December 31, 2016	2,170,000
For the year ending December 31, 2017	1,287,000
For the year ending December 31, 2018	876,000
For the year ending December 31, 2019	810,000
Core Deposit Intangibles Acquired During the Year
Core Deposit Intangibles Acquired	$ 4,199,000	$ 5,739,000
Core Deposits Intangibles | Weighted Average
Net Core Deposit Intangibles and Aggregate Amortization Expense
Weighted-average amortization period (Period in years)	9 years 7 months