Debt - Lines of Credit (Details) (Lines of credit, USD $)	3 Months Ended
	Mar. 31, 2015
Credit Facilities
Line of Credit Facility [Line Items]
Maximum borrowing capacity	150,000,000.0
Letters of credit, amount outstanding	6,200,000
Credit Facilities | Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.375%
Revolving Credit Facility | Credit Facilities
Line of Credit Facility [Line Items]
Maximum debt to adjusted EBITDA ratio	2.50
Minimum EBITDA to interest expense ratio	3.0
Revolving Credit Facility | Credit Facilities | Federal Funds Effective Rate
Line of Credit Facility [Line Items]
Description of variable rate basis	Federal Funds Effective Rate
Fixed spread on variable rate	0.50%
Revolving Credit Facility | Credit Facilities | Eurodollar
Line of Credit Facility [Line Items]
Description of variable rate basis	Eurodollar rate
Fixed spread on variable rate	1.00%
Revolving Credit Facility | Credit Facilities | Eurodollar | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Variable spread on variable rate	0.50%
Revolving Credit Facility | Credit Facilities | Eurodollar | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.50%
Variable spread on variable rate	1.50%
Revolving Credit Facility | Revolving Credit Facility Maturing August 2018
Line of Credit Facility [Line Items]
Maximum borrowing capacity limit	100,000,000.0
Letter of Credit | Revolving Credit Facility Maturing August 2018
Line of Credit Facility [Line Items]
Maximum borrowing capacity limit	20,000,000.0
Swing Line Loan | Revolving Credit Facility Maturing August 2018
Line of Credit Facility [Line Items]
Maximum borrowing capacity limit	10,000,000.0