Share-Based Compensation Stock options (Details) (Stock Options [Member], USD $)	3 Months Ended
	Mar. 31, 2013
Stock option transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2012	770,923
Exercised	(50,750)
Balance at March 31, 2013	720,173
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at December 31, 2012	$ 11.35
Exercised	$ 4.37
Balance at March 31, 2013	$ 11.84
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Options Outstanding, Number outstanding at end of period	720,173
Options Outstanding, Weighted-average remaining term (in years and months)	2 years 11 months
Options Exercisable, Number exercisable at end of period	720,173
Options Exercisable, Weighted-average exercise price	$ 11.84
Stock options, additional disclosures [Abstract]
Unvested stock options decrease in period (in shares)	29,398
Number of unvested options at end of period (in shares)	0
$7.84 - $11.40 [Member]
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at March 31, 2013	$ 10.52
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Options Outstanding, Number outstanding at end of period	404,174
Options Outstanding, Weighted-average remaining term (in years and months)	2 years 7 months
Options Exercisable, Number exercisable at end of period	404,174
Options Exercisable, Weighted-average exercise price	$ 10.52
$13.10 - $17.35 [Member]
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at March 31, 2013	$ 13.54
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Options Outstanding, Number outstanding at end of period	315,999
Options Outstanding, Weighted-average remaining term (in years and months)	3 years 3 months
Options Exercisable, Number exercisable at end of period	315,999
Options Exercisable, Weighted-average exercise price	$ 13.54
Minimum [Member]
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at December 31, 2012	$ 4.37
Exercised
Balance at March 31, 2013	$ 7.84
Minimum [Member] | $7.84 - $11.40 [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Range of exercise prices, lower limit	$ 7.84
Minimum [Member] | $13.10 - $17.35 [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Range of exercise prices, lower limit	$ 13.10
Maximum [Member]
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at December 31, 2012	$ 17.35
Exercised	$ 4.37
Balance at March 31, 2013	$ 17.35
Maximum [Member] | $7.84 - $11.40 [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Range of exercise prices, upper limit	$ 11.40
Maximum [Member] | $13.10 - $17.35 [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Range of exercise prices, upper limit	$ 17.35