Stock-Based Compensation (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Based Compensation [Line Items]
Shares representing outstanding award	185,450
Deferred income tax expense (benefit)	$ (113,000)	$ (285,000)	$ 716,000
Unrecognized compensation cost	300,000
Weighted average remaining service period of nonvested awards	1 year 6 months 0 days
Proceeds from issuance of common stock	102,000	63,000	284,000
Number of stock options settled for fully vested shares	327,100	44,800	782,980
Number of shares issued in settlement of stock option	140,544	17,048	214,624
Intrinsic value of stock options exercised	7,000,000	700,000	6,500,000
Income tax benefits	15,725,000	14,732,000	13,114,000
Vesting term			4 years 6 months
Restricted Stock Units (Rsus) [Member]
Stock Based Compensation [Line Items]
Unrecognized compensation cost	5,800,000
Weighted average remaining service period of nonvested awards	3 years 6 months
Vesting term	5 years
Total intrinsic value of vested RSU's	1,600,000	1,200,000	1,700,000
Stock Option [Member]
Stock Based Compensation [Line Items]
Deferred income tax expense (benefit)	700,000	500,000	600,000
Equity Option [Member]
Stock Based Compensation [Line Items]
Income tax benefits	$ 2,500,000	$ 400,000	$ 2,000,000
2011 Plan [Member]
Stock Based Compensation [Line Items]
Number of shares authorized	1,355,764
Shares reserved for future issuance	973,588
Number of outstanding awards	306,784