Credit Facilities and Restricted Cash - Credit Facilities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Credit Agreement [Member]
Line of Credit Facility [Line Items]
Line of credit facility, expiration date	Apr. 26, 2016
Line of credit facility, amount outstanding	$ 0
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	100.0
Line of credit facility, additional borrowing capacity	50.0
Line of credit facility, maximum borrowing capacity	150.0
Credit Agreement Subfacility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 50.0