Convertible Notes (Summary of Convertible Notes) (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2012	Sep. 30, 2013	Sep. 30, 2013	Aug. 01, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Principal amount a $5 incentive cash payment per each to convert debt		$ 1,000
Convertible Notes Payable, Carrying Value		318,081,000	318,081,000		309,952,000
Series 2012 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.875%
Debt Instrument, Convertible, Conversion Ratio		179.777
Convertible notes, conversion price (in Dollars per Share)		$ 5.56	$ 5.56
Principal amount a $5 incentive cash payment per each to convert debt	1,000	1,000
Convertible Notes, Maturity Date (Date)			Feb. 15, 2015
Convertible Notes, Principal Balance Outstanding		180,000,000	180,000,000	180,000,000	179,000,000
Convertible Notes Payable, Carrying Value		171,066,000	171,066,000		165,528,000
May 2015 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.75%	3.75%
Debt Instrument, Convertible, Conversion Ratio		157.3700
Convertible notes, conversion price (in Dollars per Share)		$ 6.35	$ 6.35
Convertible Notes, Maturity Date (Date)			May 01, 2015
Convertible Notes, Principal Balance Outstanding		155,250,000	155,250,000		155,250,000
Convertible Notes Payable, Carrying Value		147,015,000	147,015,000		143,433,000
February 2015 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.875%
Principal amount a $5 incentive cash payment per each to convert debt	1,000
Convertible Notes, Maturity Date (Date)			Feb. 15, 2015
Convertible Notes, Principal Balance Outstanding		0	0
Convertible Notes Payable, Carrying Value					$ 991,000