Stock-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Intrinsic value (in dollars per share)	$ 19.41
Proceeds from exercise of options	$ 170,000	$ 1,691,000	$ 1,068,000
Total intrinsic value of options exercised	676,000	11,509,000	8,050,000
Fair value assumptions [Abstract]
Weighted average grant date fair value - grants (in dollars per share)	$ 19.24	$ 23.17	$ 21.43
General and Administrative Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense	7,563,000	6,162,000	4,367,000
Restricted Stock [Member]
Options activity [Roll Forward]
Outstanding at beginning of period (in shares)	151,665	0
Options granted (in shares)	156,415	151,665
Options vested (in shares)	(55,832)
Options cancelled (in shares)	(3,333)
Outstanding at end of period (in shares)	248,915	151,665
Options, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted average exercise price, at beginning of period (in dollars per share)	$ 25.60	$ 0
Options granted, weighted average exercise price - options granted (in dollars per share)	$ 23.72	$ 26
Options vested, weighted average exercise price (in dollars per share)	$ 27.06
Options, weighted average exercise price, options cancelled (in dollars per share)	$ 24.75
Outstanding, weighted average exercise price, balance at end of period (in dollars per share)	$ 24.10	$ 25.60
Options outstanding, aggregate intrinsic value	0	0
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Aggregate intrinsic value of options exercisable	63,490,000
Total compensation cost not yet recognized, Total	11,752,000
Total compensation cost not yet recognized, period for recognition	2 years 4 months 20 days
Fair value assumptions [Abstract]
Expected stock price volatility (in hundredths)	93.00%	111.00%	123.00%
Risk free interest rate (in hundredths)	2.04%	1.90%	3.05%
Expected life term (in years)	6 years 1 month 6 days	6 years 9 months 18 days	6 years 7 months 6 days
Expected dividend	0	0	0
Options activity [Roll Forward]
Outstanding at beginning of period (in shares)	4,776,224	4,906,998	4,830,391
Options granted (in shares)	274,625	367,500	475,000
Options exercised (in shares)	(39,833)	(486,165)	(398,393)
Options cancelled (in shares)	(34,167)	(12,109)	0
Outstanding at end of period (in shares)	4,976,849	4,776,224	4,906,998
Options, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted average exercise price, at beginning of period (in dollars per share)	$ 6.94	$ 5.12	$ 3.14
Options granted, weighted average exercise price - options granted (in dollars per share)	$ 25.37	$ 26.97	$ 23.80
Options exercised, weighted average exercise price (in dollars per share)	$ 4.27	$ 3.48	$ 2.68
Options, weighted average exercise price, options cancelled (in dollars per share)	$ 20.57	$ 17.34	$ 0
Outstanding, weighted average exercise price, balance at end of period (in dollars per share)	$ 7.86	$ 6.94	$ 5.12
Options outstanding, weighted average remaining contractual term, at end of period	4 years 10 months 28 days
Options outstanding, aggregate intrinsic value	63,649
Stock Options [Member] | General and Administrative Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense	6,488,000	5,171,000	4,367,000
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Aggregate intrinsic value of options exercisable	0
Total compensation cost not yet recognized, Total	4,773,000
Total compensation cost not yet recognized, period for recognition	2 years 8 months 12 days
Options activity [Roll Forward]
Outstanding at end of period (in shares)	248,915
Options, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted average exercise price, balance at end of period (in dollars per share)	$ 24.10
Restricted Stock Units (RSUs) [Member] | General and Administrative Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated Share-based Compensation Expense	$ 1,075,000	$ 991,000	$ 0