Condensed Consolidating Financial Statements of Guarantors of Senior Notes and Senior Convertible Notes Condensed Consolidating Statements of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Net income	$ 28,552	$ 27,394	$ 34,435	$ 58,722	$ 26,384	$ 41,797	$ 37,639	$ 48,315	$ 149,104	$ 154,135	$ 146,232
Other comprehensive income									(28,532)	4,276	(8,245)
Total comprehensive income attributable to common stockholders									120,572	158,411	137,987
Parent
Condensed Financial Statements, Captions [Line Items]
Net income									143,848	152,546	144,903
Other comprehensive income									(23,276)	5,865	(6,916)
Total comprehensive income attributable to common stockholders									120,572	158,411	137,987
Subsidiary Issuer
Condensed Financial Statements, Captions [Line Items]
Net income									505
Other comprehensive income									0
Total comprehensive income attributable to common stockholders									505
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income									1,025
Other comprehensive income									0
Total comprehensive income attributable to common stockholders									1,025
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income									253,578	251,392	230,865
Other comprehensive income									(23,276)	5,865	(6,916)
Total comprehensive income attributable to common stockholders									230,302	257,257	223,949
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net income									(249,852)	(249,803)	(229,536)
Other comprehensive income									18,020	(7,454)	5,587
Total comprehensive income attributable to common stockholders									$ (231,832)	$ (257,257)	$ (223,949)