Stock-Based Compensation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ (3,749)	$ 3,416	$ 3,661	$ 11,135
Share-based payment award [Roll forward]
Beginning balance (in shares)			285
Granted (in shares)			134
Vested (in shares)			0
Forfeited (in shares)			0
Ending balance (in shares)	419		419
Additional disclosure [Abstract]
Weighted average grant date fair value, beginning balance (in dollars per share)			$ 37.93
Weighted average grant date fair value, granted (in dollars per share)			$ 71.52
Weighted average grant date fair value, vested (in dollars per share)			$ 0
Weighted average grant date fair value, forfeited (in dollars per share)			$ 0
Weighted average grant date fair value, ending balance (in dollars per share)	$ 48.69		$ 48.69
Aggregate intrinsic value of units outstanding	9,793		9,793
Maximum number of common stock shares to be issued (in shares)	403	443	403	443
PRSUs Benefit related to PRSU's granted in 2011 and 2012	7,974		9,536
Share-based payment award options outstanding [Roll Forward]
Beginning Balance (in shares)			3,408
Granted (in shares)			98
Forfeited (in shares)			0
Exercised (in shares)			840
Ending balance (in shares)	2,666		2,666
Options exercisable (in shares)	2,090		2,090
Unvested stock options additional disclosure [Abstract]
Beginning of period weighted average grant date fair value (dollars per share)			$ 11.15
Granted weighted average grant date fair value (dollars per share)			$ 70.24
Forfeited weighted average grant date fair value (dollars per share)			$ 0
Exercised weighted average grant date fair value (dollars per share)			$ 12.56
Ending of period weighted average grant date fair value (dollars per share)	$ 15.98		$ 15.98
Options exercisable Weighted average grant date fair value (in dollars per share)	$ 13.88		$ 13.88
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Ending balance weighted average remaining contractual term (in years)			5 years 10 months 28 days
Options exercisable weighted average remaining contractual term (in years)			5 years 6 months 18 days
Ending balance aggregate intrinsic value	18,975		18,975
Options exercisable aggregate intrinsic value	19,868		19,868
Total intrinsic value of options exercised	770	10,961	32,206	70,276
Total unrecognized stock-based compensation expense	2,886		2,886
Weighted Average Remaining Vesting Period (in years)			2 years 18 days
Performance based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	(5,207)	1,708	(1,126)	5,719
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	911	1,237	3,169	3,931
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Total unrecognized stock-based compensation expense	2,526		2,526
Weighted Average Remaining Vesting Period (in years)			2 years 3 months 4 days
Restricted Stock Units And Deferred Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	547	471	1,618	1,485
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Total unrecognized stock-based compensation expense	$ 360		$ 360
Weighted Average Remaining Vesting Period (in years)			6 months 29 days