Borrowing Arrangements - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Sep. 27, 2010	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Primary debt arrangements		2
Unsecured credit facility		$ 275,000,000
Group of participating banks		7
Outstanding balance under the credit facility		40,000,000	208,900,000
Approximately available funds under credit facility		138,800,000
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
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
Amortized discount at annual effective rate	7.50%
Discount, period of issuance	5 years
Remaining period for amortization of discount		24 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	$ 750,000