Debt (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Less current maturities	$ (202,401)	$ (2,428)
Carrying Amount [Member]
Debt Instrument [Line Items]
Total debt	766,283	216,243
Less current maturities	(202,401)	(2,428)
Long-term debt	563,882	213,815
Estimated Fair Value [Member]
Debt Instrument [Line Items]
Total debt	787,345	230,965
Less current maturities	(219,753)	(2,428)
Long-term debt	567,592	228,537
Senior Notes [Member] | Carrying Amount [Member] | 6.35% Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	200,000	204,028
Senior Notes [Member] | Carrying Amount [Member] | 3.875% Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	273,732	0
Senior Notes [Member] | Carrying Amount [Member] | 4.375% Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	273,961	0
Senior Notes [Member] | Estimated Fair Value [Member] | 6.35% Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	217,352	218,750
Senior Notes [Member] | Estimated Fair Value [Member] | 3.875% Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	274,973	0
Senior Notes [Member] | Estimated Fair Value [Member] | 4.375% Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	276,430	0
Capital Leases [Member] | Carrying Amount [Member]
Debt Instrument [Line Items]
Total debt	18,590	12,215
Capital Leases [Member] | Estimated Fair Value [Member]
Debt Instrument [Line Items]
Total debt	$ 18,590	$ 12,215