Stock Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-Based Compensation (Details) [Line Items]
Stock-based compensation expense	$ 6,559,000	$ 6,456,000	$ 8,366,000
Stock-based compensation expense, tax benefit	2,117,000	2,464,000	3,022,000
Stock-based compensation expense, net of tax	4,442,000	3,992,000	5,344,000
Vesting % of performance based restricted stock units, maximum	200.00%
Restricted Stock Unit Activity (Table Details) [Abstract]
Number of nonvested restricted stock units outstanding	635,573	516,672
Granted	375,834
Vested	73,524
Forfeited	183,409
Weighted average grant date fair value, outstanding	$ 28.53	$ 32.69
Weighted average grant date fair value, granted	$ 23.16
Weighted average grant date fair value, vested	$ 28.95
Weighted average grant date fair value, forfeited	$ 29.02
Stock Option Activity (Table Details) [Abstract]
Number of awards outstanding	2,625,964	2,331,157
Granted	1,024,057
Exercised	211,617
Forfeited	400,884
Expired	116,749
Exercisable	1,017,677
Weighted Average Exercise Price [Abstract]
Equity awards outstanding	$ 30.63	$ 31.36
Granted	$ 28.41
Exercised	$ 21.86
Forfeited	$ 32.92
Expired	$ 33.28
Exercisable	$ 29.12
Weighted Average Remaining Contractual Life [Abstract]
Equity awards outstanding	7 years 2 months 29 days
Exercisable	5 years 2 months 17 days
Aggregate Intrinsic Value [Abstract]
Equity awards outstanding	16,045,000
Exercisable	7,750,000
Exercised	1,900,000	5,800,000	7,500,000
Excess tax benefits related to stock awards	331,000	406,000	4,348,000
Assumptions Used in Fair Value Calculation of Stock Options (Table Details) [Abstract]
Valuation method used	Black-Scholes	Black-Scholes	Binomial
Risk free interest rate, weighted average	1.54%	0.88%	0.35%
Expected dividend yield, weighted average	3.28%	2.34%	1.74%
Expected life, weighted average	5 years	4 years 5 months 6 days	6 years 3 months
Expected volatility, weighted average	34.77%	37.88%	39.72%
Weighted average grant date fair value	$ 6.49	$ 9.27	$ 10.08
Prior Plan [Member]
Stock-Based Compensation (Details) [Line Items]
Number of shares authorized to issue	14,562,865
Stock Option Activity (Table Details) [Abstract]
Number of awards outstanding	48,349	97,499
Equity Incentive Plan [Member]
Stock-Based Compensation (Details) [Line Items]
Number of shares authorized to issue	2,468,461
Stock Option Activity (Table Details) [Abstract]
Number of awards outstanding	1,269,197	1,020,361
2006 Plan [Member]
Stock-Based Compensation (Details) [Line Items]
Number of shares authorized to issue	7,000,000
Stock Option Activity (Table Details) [Abstract]
Number of awards outstanding	1,955,950	1,729,969
Employee Stock Option [Member]
Stock-Based Compensation (Details) [Line Items]
Unvested awards - to result in compensation expense	8,300,000
Weighted average number of years to vesting	2 years 6 months 27 days
Stock-based compensation expense	5,044,000	3,944,000	3,915,000
Exercise period of options once vested	10 years
Employee Stock Option [Member] | Minimum [Member]
Stock-Based Compensation (Details) [Line Items]
Vesting period of options granted	1 year
Employee Stock Option [Member] | Maximum [Member]
Stock-Based Compensation (Details) [Line Items]
Vesting period of options granted	4 years
Restricted Stock Units (RSUs) [Member]
Stock-Based Compensation (Details) [Line Items]
Unvested awards - to result in compensation expense	2,500,000
Weighted average number of years to vesting	1 year 8 months 24 days
Stock-based compensation expense	$ 1,515,000	$ 2,512,000	$ 4,451,000
Restricted Stock Units (RSUs) [Member] | 2006 Plan [Member]
Stock-Based Compensation (Details) [Line Items]
Number of shares authorized to issue	3,500,000