Borrowing Arrangements - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended
	Sep. 27, 2010 Days	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Primary debt arrangements		2
Unsecured credit facility		$ 275,000,000
Group of participating banks		7
Outstanding balance under credit facility		91,400,000	48,500,000
Approximately available funds under credit facility		62,100,000
Maturity date of credit facility		2015-06
Letter of Credit and Performance Guarantee [Member]
Debt Instrument [Line Items]
Outstanding letters of credit and performance guarantees		4,400,000
2010 Convertible Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Convertible Senior Subordinated Notes	130,000,000	130,000,000
Unsecured credit facility		275,000,000
Interest rate on Notes	4.875%
Notes payable terms		Semi-annually in arrears on April 1 and October 1
Maturity date of Notes	Oct. 01, 2015
Debt instrument, convertible, Date	Jul. 31, 2015
Debt Instrument, convertible, least trading days	20
Debt instrument, convertible, consecutive trading days	30 days
Debt instrument, convertible, minimum percentage of stock price	135.00%
Amortized discount at annual effective rate	7.50%
Discount, period of issuance	5 years
Remaining period for amortization of discount		18 months
Principal amount of notes		130,000,000	130,000,000
2006 Convertible Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Interest rate on Notes		3.125%
Notes payable terms		Semi-annually in arrears on each June 1 and December 1
Maturity date of Notes		Jun. 01, 2026
Principal amount of notes		$ 750,000