Long Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified		9 Months Ended		0 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 Forward Starting Interest Rate Swap Agreement	Sep. 03, 2014 Forward Starting Interest Rate Swap Agreement	Jun. 05, 2014 Forward Starting Interest Rate Swap Agreement	Sep. 30, 2014 2013 Refinancing Credit Agreement	Sep. 30, 2014 2013 Refinancing Credit Agreement Base Rate	Sep. 30, 2014 2013 Refinancing Credit Agreement Base Rate Minimum	Sep. 30, 2014 2013 Refinancing Credit Agreement Base Rate Maximum	Sep. 30, 2014 2013 Refinancing Credit Agreement Alternative Rate	Sep. 30, 2014 2013 Refinancing Credit Agreement Alternative Rate Minimum	Sep. 30, 2014 2013 Refinancing Credit Agreement Alternative Rate Maximum	Sep. 30, 2014 2011 Refinancing Credit Agreement	Sep. 30, 2014 2011 Refinancing Credit Agreement Base Rate	Sep. 30, 2014 2011 Refinancing Credit Agreement Base Rate Minimum	Sep. 30, 2014 2011 Refinancing Credit Agreement Base Rate Maximum	Sep. 30, 2014 2011 Refinancing Credit Agreement Alternative Rate	Sep. 30, 2014 2011 Refinancing Credit Agreement Alternative Rate Minimum	Sep. 30, 2014 2011 Refinancing Credit Agreement Alternative Rate Maximum	Sep. 30, 2014 4.375% Senior Notes, due 2023	Sep. 30, 2014 6.875% Senior Notes, Due 2013	Sep. 30, 2014 Revolving Credit Facility 2013 Refinancing Credit Agreement	Sep. 30, 2014 Revolving Credit Facility 2011 Refinancing Credit Agreement	Sep. 30, 2014 Letter of Credit
Debt Instrument [Line Items]
Revolving credit facility, amount																					$ 800	$ 600
Credit facility loan term, years																					5 years	5 years
Deferred financing cost					1.0														2.6			1.9
Debt instrument, effective issuance date		Jul. 31, 2013		Nov. 07, 2016	Dec. 19, 2013							Nov. 07, 2011							Aug. 31, 2013	Aug. 31, 2003
Maturity date of debt instrument					Dec. 19, 2018							Nov. 07, 2016
Line of credit facility, current borrowing capacity																							17.0
Line of credit facility, amount currently available																					513.0
Debt instrument, interest rate, effective percentage					0.50%							0.50%
Debt instrument basis points spread on variable rate					1.00%	0.00%	0.00%	0.75%	0.75%	0.75%	1.75%	1.00%	0.00%	0.00%	0.75%	1.00%	0.75%	1.75%
Long-term debt, percentage bearing variable interest rate	1.16%
Maturity date of debt instrument		Nov. 07, 2016		Dec. 19, 2018																Jul. 31, 2013
Interest rate swap agreements, notional amount		150.0		150.0
Interest rate on notional value			1.415%	2.56%
Minimum interest expense coverage ratio					3.0
Maximum debt to cash flow ratio					3.25
Senior Notes Coupon Rate																			99.879%
Maturity date of debt instrument, year																			2023
Senior Notes issued																			$ 250.0	$ 150.0
Debt Instrument, Interest Rate, Stated Percentage																			4.375%	6.875%