Net Carrying Amount of Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Long term debt	$ 1,394,077		$ 1,401,783		$ 1,411,122		$ 1,419,084		$ 1,427,319
Senior Secured Notes
Debt Instrument [Line Items]
Long term debt	774,030		789,311		806,263		821,575		836,888
1.50% Convertible Notes
Debt Instrument [Line Items]
Long term debt	339,943	[1]	335,772	[2]	331,563	[3]	327,354	[4]	323,418
2.50% Convertible Notes
Debt Instrument [Line Items]
Long term debt	$ 280,104	[5]	$ 276,700	[6]	$ 273,296	[7]	$ 270,155	[8]	$ 267,013

[1] Reflects the net debt carrying amount of the 1.50% Convertible Notes in the consolidated balance sheet as of December 31, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 1.50% Convertible Notes is $400.0 million.

[2] Reflects the net debt carrying amount of the 1.50% Convertible Notes in the consolidated balance sheet as of September 30, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 1.50% Convertible Notes is $400.0 million.

[3] Reflects the net debt carrying amount of the 1.50% Convertible Notes in the consolidated balance sheet as of June 30, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 1.50% Convertible Notes is $400.0 million.

[4] Reflects the net debt carrying amount of the 1.50% Convertible Notes in the consolidated balance sheet as of March 31, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 1.50% Convertible Notes is $400.0 million.

[5] Reflects the net debt carrying amount of the 2.50% Convertible Notes in the consolidated balance sheet as of December 31, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 2.50% Convertible Notes is $300.0 million.

[6] Reflects the net debt carrying amount of the 2.50% Convertible Notes in the consolidated balance sheet as of September 30, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 2.50% Convertible Notes is $300.0 million.

[7] Reflects the net debt carrying amount of the 2.50% Convertible Notes in the consolidated balance sheet as of June 30, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 2.50% Convertible Notes is $300.0 million.

[8] Reflects the net debt carrying amount of the 2.50% Convertible Notes in the consolidated balance sheet as of March 31, 2014, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 2.50% Convertible Notes is $300.0 million.