Income Taxes (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Income taxes
Net deferred tax liabilities	$ 266,700,000		$ 298,900,000
Effective income tax rate (as a percent)	17.30%
Expense (benefit) from income taxes	(1,546,000)	(24,067,000)
Deferred expense (benefit) from income taxes	32,408,000	39,592,000
Out of period adjustment
Income taxes
Effective income tax rate (as a percent)	(14.80%)
Expense (benefit) from income taxes	1,200,000
Current expense (benefit) from income taxes	19,500,000
Deferred expense (benefit) from income taxes	18,300,000
State
Income taxes
Valuation allowance	21,400,000		19,700,000
United Kingdom operations
Income taxes
Valuation allowance	$ 19,800,000		$ 19,600,000