Financing Agreements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified			0 Months Ended					9 Months Ended	0 Months Ended					9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended			0 Months Ended		9 Months Ended	0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Mar. 22, 2012 Second Amended Restated Credit Agreement	Mar. 22, 2012 Second Amended Restated Credit Agreement	Mar. 22, 2012 Second Amended Restated Credit Agreement Minimum	Mar. 22, 2012 Second Amended Restated Credit Agreement Maximum	Sep. 30, 2014 Amended and Restated Credit Agreement	Sep. 30, 2014 London Interbank Offered Rate (LIBOR)	Mar. 22, 2012 London Interbank Offered Rate (LIBOR) Second Amended Restated Credit Agreement	Mar. 22, 2012 London Interbank Offered Rate (LIBOR) Second Amended Restated Credit Agreement Minimum Scenario 1	Mar. 22, 2012 London Interbank Offered Rate (LIBOR) Second Amended Restated Credit Agreement Minimum Scenario 2	Mar. 22, 2012 London Interbank Offered Rate (LIBOR) Second Amended Restated Credit Agreement Maximum Scenario 1	Mar. 22, 2012 London Interbank Offered Rate (LIBOR) Second Amended Restated Credit Agreement Maximum Scenario 2	Sep. 30, 2014 Federal Funds Rate	Mar. 22, 2012 Federal Funds Rate Second Amended Restated Credit Agreement	Sep. 30, 2014 Prime Lending Rate	Oct. 22, 2014 Subsequent Event 3.50% Convertible Senior Notes Due 2019	Oct. 22, 2014 Subsequent Event 3.50% Convertible Senior Notes Due 2019	Mar. 22, 2012 Senior Unsecured Revolving Credit Facility Second Amended Restated Credit Agreement	Mar. 22, 2012 Senior Unsecured Revolving Credit Facility Second Amended Restated Credit Agreement Minimum	Mar. 22, 2012 Senior Unsecured Revolving Credit Facility Second Amended Restated Credit Agreement Maximum	Sep. 30, 2014 Senior Unsecured Revolving Credit Facility Amended and Restated Credit Agreement	Mar. 22, 2012 Senior Unsecured Revolving Credit Facility Letter of Credit Second Amended Restated Credit Agreement Minimum	Mar. 22, 2012 Senior Unsecured Revolving Credit Facility Letter of Credit Second Amended Restated Credit Agreement Maximum	Sep. 30, 2014 Senior Unsecured Revolving Credit Facility Letter of Credit Amended and Restated Credit Agreement	Mar. 22, 2012 Term Loan Facility Second Amended Restated Credit Agreement	Sep. 30, 2014 Term Loan Facility Second Amended Restated Credit Agreement Fourth Quarter	Sep. 30, 2014 Term Loan Facility Amended and Restated Credit Agreement
Line of Credit Facility [Line Items]
Maximum borrowings under senior unsecured revolving credit facility				$ 325,000															$ 225,000							$ 100,000
Debt instrument maturity date			Mar. 22, 2015														Oct. 15, 2019
Amortization payments on outstanding principal amount of term loans, in next twelve months																											2,500
Debt instrument, basis spread on variable rate								0.15%	1.00%	2.50%	1.50%	3.25%	2.25%	0.07%	0.50%	3.25%
Fee on all outstanding amounts of letters of credit																							2.50%	3.25%
Commitment fee on the unused portion of the revolving credit facility																				0.35%	0.50%
Consolidated Leverage Ratio						300.00%
Interest Charge Coverage Ratio					300.00%
Utilized portion of credit facility							200,600															118,100			309			82,500
Credit facility due to mature																						Mar. 22, 2015
Credit facility, available to be utilized																						86,775
Credit facility, available to be utilized after restriction																						80,451
Interest rate at the end of period, effective								3.16%
Debt instrument, interest rate																		3.50%
Utilized portion of credit facility, classified in Current portion of long-term debt	$ 10,000	$ 9,375																				$ 10,000