Subsequent Events (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		0 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jul. 23, 2013 Subsequent Event	Jul. 23, 2013 Subsequent Event 2011 Credit Agreement	Jul. 23, 2013 Subsequent Event 2011 Credit Agreement Greater than	Jul. 23, 2013 Subsequent Event 2011 Credit Agreement High end of range
Subsequent Event
Increase in interest margin from existing levels (as a percent)						1.00%
Additional minimum liquidity covenant amount						$ 225.0
Senior secured leverage ratio (as a percent)							5.50
Additional capital expenditures covenant amount in 2013						175.0
Additional capital expenditures covenant amount in 2014						200.0
Potential unused capital spending that may be carried forward								20.0
Increased capital expenditures covenant amount in 2014, if carryforward from prior year is utilized								220.0
Mandatory repayment percentage of net cash proceeds from incurrence and issuance of unsecured indebtedness						100.00%
First amount of indebtedness that is required to be mandatorily repaid for the incurrence or issuance of unsecured indebtedness						$ 250.0
Secured leverage ratio requirement for restriction on cash dividends allowed in any fiscal quarter						4.50
Quarterly dividend announced by Company due to current market conditions and fifth amendment to credit agreement					$ 0.01
Most recent quarterly dividend (in dollars per share)	$ 0.125	$ 0.125	$ 0.25	$ 0.25