Employee Benefit and Deferred Compensation Plans - (Details Textual)	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) shares	Jun. 30, 2014 USD ($) shares	Jun. 30, 2015 USD ($) Point shares	Jun. 30, 2014 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Retiring age limit, minimum			55 years
Retiring age limit, maximum			65 years
Eligible employee years of service (in years)			15 years
Number of points for eligibility | Point			70
Minimum Eligible Age for Medicare Coverage			65 years
Life Insurance Coverage Face Value | $			$ 5
Life Insurance Coverage Age Maximum			70 years
Life Insurance Coverage at Retiree Expense after Age			70 years
Option expiration period (in years)			10 years
Award vesting period (in years)			3 years
Option exercisable period (in years)			3 years
Treasury shares reissued (shares)			99,561
Total stock-based compensation expense | $	$ 857,000	$ 951,000	$ 1,720,000	$ 1,822,000
Stock options granted (shares)	0	0	0	0
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period			1 year