Convertible Notes (Summary of Convertible Notes) (Detail) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended
	Jan. 31, 2012	Jun. 30, 2013	Jun. 30, 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		315,320,000	315,320,000	309,952,000
Series 2012 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.875%	7.30%	7.30%
Debt Instrument, Convertible, Conversion Ratio		176.389
Convertible notes, conversion price (in Dollars per Share)		$ 5.67	$ 5.67
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		179,000,000	179,000,000	179,000,000
Convertible Notes Payable, Carrying Value		168,528,000	168,528,000	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		154.4189
Convertible notes, conversion price (in Dollars per Share)		$ 6.48	$ 6.48
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		145,799,000	145,799,000	143,433,000
February 2015 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.875%
Debt Instrument, Convertible, Conversion Ratio		176.389
Convertible notes, conversion price (in Dollars per Share)		$ 5.67	$ 5.67
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		1,000,000	1,000,000
Convertible Notes Payable, Carrying Value		$ 993,000	$ 993,000	$ 991,000