Equity-Based Compensation (Narrative) (Details) (USD $)	9 Months Ended		12 Months Ended	9 Months Ended		12 Months Ended			9 Months Ended		12 Months Ended	9 Months Ended			12 Months Ended
	Sep. 30, 2013 Y	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 2005 Equity Incentive Plan [Member]	Sep. 30, 2013 Performance Stock Units [Member]	Dec. 31, 2012 Performance Stock Units [Member]	Jan. 31, 2013 Performance Stock Units [Member]	Jan. 31, 2012 Performance Stock Units [Member]	Sep. 30, 2013 Management Stock Purchase Plan [Member]	Sep. 30, 2012 Management Stock Purchase Plan [Member]	Dec. 31, 2012 Management Stock Purchase Plan [Member]	Sep. 30, 2013 Minimum [Member] Performance Stock Units [Member]	Sep. 30, 2013 Maximum [Member] Performance Stock Units [Member]	Sep. 30, 2013 Unvested Restricted Stock Units [Member]	Dec. 31, 2012 Unvested Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued under the Plan				3,000,000
Maximum number of shares that may be issued in connection with grants of incentive stock options and rights				900,000
Performance stock units outstanding					246,000	280,000	304,000	295,000
Performance stock unit grant-date fair value							$ 4,123,000	$ 4,152,000
Performance stock unit vesting period												1 year	3 years
Percentage of target performance stock units earned						58.30%
Performance stock units earned						163,200
Performance stock units target awards						280,000
Years of service					5 years
Average closing price, number of days trailing					90 days				200 days
Weighted average fair value of per unit awarded									$ 16.09		$ 12.30
Number of restricted stock units credited to participant accounts	604,339		777,159						121,488	237,613				46,866	71,992
MSPP company matching portion, vesting age	60
Accrues interest									2.00%
Disbursements of MSPP	$ 531,000	$ 542,000