Long-Term Debt (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Repayment of convertible notes		$ 186,956,000
Shares issued in conjunction with the conversion feature of the Notes		249,000
Stock received in written call transaction		266,000
Number of shares called by warrants	2,477,000	2,477,000
Warrants settled and recorded as an adjustment to paid in capital	2,600,000
Average stock price per share to make warrants dilutive		$ 102.20
Standby letters of credit issued	36,900,000	36,900,000
Unused lines of credit	253,100,000	253,100,000
2014 Credit Agreement [Member]
Debt Instrument [Line Items]
Debt instrument term		5 years
Deferred financing costs	900,000	900,000
2014 Credit Agreement [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable interest rate		1.25%
2014 Credit Agreement [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Face amount of debt	350,000,000	350,000,000
2014 Credit Agreement [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 100,000,000	$ 100,000,000