Shareholders' Equity (Details 4) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
RSUs
Awards Outstanding
Balance at the beginning of the period (in shares)	747	981	901
Granted (in shares)	310	98	369
Issued (in shares)	(238)	(287)	(275)
Forfeited (in shares)	(34)	(45)	(14)
Balance at the end of the period (in shares)	785	747	981	901
Balance at the beginning of the period (in dollars per share)	$ 35.61	$ 34.06	$ 25.59
Granted (in dollars per share)	$ 44.34	$ 40.59	$ 40.98
Issued (in dollars per share)	$ 36.67	$ 32.00	$ 16.12
Forfeited (in dollars per share)	$ 40.25	$ 35.92	$ 30.74
Balance at the end of the period (in dollars per share)	$ 38.55	$ 35.61	$ 34.06	$ 25.59
Aggregate Intrinsic Value	$ 36,872,000	$ 31,775,000	$ 39,888,000	$ 37,373,000
Weighted Average Remaining Vesting Term	1 year 6 months	1 year 3 months 18 days	1 year 6 months	1 year 8 months 12 days
Aggregate intrinsic value of awards issued	10,100,000	11,300,000	11,600,000
SSAR Awards
Awards Outstanding
Balance at the beginning of the period (in shares)	272	422	517
Granted (in shares)		218
Issued (in shares)	0		0
Exercised (in shares)	(36)	(366)	(95)
Forfeited (in shares)	(4)	(2)
Balance at the end of the period (in shares)	232	272	422	517
Balance at the beginning of the period (in dollars per share)	$ 37.69	$ 15.30	$ 15.06
Granted (in dollars per share)		$ 41.42
Exercised (in dollars per share)	$ 22.26	$ 14.07	$ 16.76
Forfeited (in dollars per share)	$ 40.91	$ 37.34
Balance at the end of the period (in dollars per share)	$ 40.06	$ 37.69	$ 15.30	$ 15.06
Aggregate Intrinsic Value	1,595,000	1,594,000	10,927,000	13,921,000
Weighted Average Remaining Vesting Term	3 years	3 years 7 months 6 days	7 months 6 days	1 year 4 months 24 days
SSAR Awards Exercisable
SSAR Awards (in shares)	54	56	322	410
Weighted Average Exercise Price (in dollars per share)	$ 35.81	$ 23.25	$ 16.02	$ 15.39
Aggregate Intrinsic Value	600,000	1,124,000	8,108,000	10,895,000
Weighted Average Remaining Contractual Life	2 years 2 months 12 days	1 year	8 months 12 days	1 year 4 months 24 days
Aggregate intrinsic value of SSAR Awards exercised	$ 800,000	$ 9,100,000	$ 2,100,000
Assumptions used to determine weighted average fair value
Weighted average fair value of SSAR Awards (in dollars per share)		$ 11.65
Expected term		4 years 1 month 6 days
Volatility (as a percent)		38.00%
Dividend yields (as a percent)		0.40%
Risk-free interest rates (as a percent)		0.60%

The aggregate intrinsic value of outstanding awards of equity-based plans excluding option plans for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units, as calculated by applying the disclosed pricing methodology.

No definition available.