Convertible Debentures and Credit Arrangements - Convertible Senior Debentures due 2018 - Additional Information (Detail) (USD $)		9 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 Convertible Senior Debentures due 2018 [Member]	Nov. 30, 2012 Convertible Senior Debentures due 2018 [Member]	Sep. 30, 2013 Convertible Senior Debentures due 2018 [Member] Minimum	Nov. 30, 2012 Convertible Senior Debentures due 2014 [Member]	Mar. 31, 2010 Convertible Senior Debentures due 2014 [Member]
Debt Instrument [Line Items]
Aggregate face value of convertible senior debentures			$ 55,000,000.0			$ 46,900,000.0
Interest rate on debentures		8.70%	5.25%		10.125%
Debt Instrument Expiration Date Year		2018
Percentage of the closing sales price of the entity's common stock that the conversion price exceeded giving the holders of the debentures an option (as a percent)				130.00%
Number of consecutive trading days during which the trading price per $1,000 principal amount for at least five days was less than 98% of the product of the closing sale price per share of Company common stock multiplied by the conversion rate on each such trading day (in days)		5 days
Number of days after five consecutive trading days in which the trading price per $1,000 principal amount was less than 98% of the product of the closing sale price per share of Company common stock multiplied by the conversion rate on each such trading day (in days)		5 days
Principal amount of convertible debentures	1,000	1,000
Closing price is percentage of conversion price		98.00%
Convertible senior debentures, convertible latest date		Nov. 15, 2017
Conversion rate of common stock		55.17
Conversion price (in dollars per share)		$ 18.13
Closing price for common stock		$ 15.69
Sales price of common stock to conversion price		140.00%
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock exceeded the conversion price giving the holders of the debentures an option (in days)		20 days
Number of consecutive trading days during which the closing price of the entity's common stock exceeded the conversion price for at least 20 days giving the holders of the debentures an option (in days)		30 days
Debentures redemption price		100.00%
Change in control due to debentures redemption		50.00%
Percentage of principal amount and accrued and unpaid interest for repurchase of debt		100.00%
Outstanding debentures		55,000,000
Fair value of Debentures outstanding		59,400,000
Gross carrying amount of equity component		6,400,000
Principal amount of liability component		55,000,000
Unamortized discount		5,800,000
Carrying value of liability component		49,200,000
Additional interest expenses		$ 700,000