SBM Acquisition (Details)		12 Months Ended
	Oct. 16, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) branch office shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($)	Oct. 16, 2015 shares	Oct. 16, 2015	Oct. 16, 2015 USD ($)	Oct. 16, 2015 branch	Oct. 15, 2015
Business Acquisition [Line Items]
Equity interest issued		$ 110,551,000	$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares | shares		11,600	21,100
Number of Branches | branch		64
number of commercial production offices | office		3
Acquisition and divestiture costs		$ 10,415,000	$ 0	374,000
Goodwill		$ 95,657,000	$ 44,806,000	$ 44,806,000
Number of companies in integration		2
SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, percentage of voting interest acquired						100.00%			80.00%
Business Acquisition, Cash Consideration, Per Share Amount | $ / shares	$ 206.00
Business Acquisition, Stock for Stock Consideration, Conversion Ratio						5.421
Total consideration paid	$ 136,700,000
Cash	$ 26,100,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares	2,749,762
Equity interest issued							$ 108,561,000
Share Price | $ / shares	$ 39.48
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares | shares					92,688
Number of Branches						4		64
number of commercial production offices						3
Core deposits (demand, checking , savings and money market accounts)							497,400,000
Acquisition and divestiture costs		$ 10,400,000
Goodwill							50,851,000
Loan interest accretion	$ 531,000
Nonqualified Stock Options [Member] | SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Business Acquisition, Stock for Stock Consideration, Conversion Ratio						5.421
Equity interest issued							$ 1,990,000