6. Long-Term Debt (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2010
Debt Instrument [Line Items]
Long-term debt	$ 435,800,000	$ 435,800,000
Less current maturities	(200,000)	(200,000)
Long-term Debt, Excluding Current Maturities	435,607,000	435,615,000
Unsecured Debt [Member] | Senior Notes 4.875% [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.875%
Long-term debt	423,300,000	423,200,000	422,600,000
Debt Instrument, Interest Rate, Effective Percentage			4.946%
Face amount of debt sold			425,000,000
Capital Lease Obligations [Member] | Debt 6 [Member]
Debt Instrument [Line Items]
Long-term debt	12,500,000	12,600,000
Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity	200,000,000
Outstanding borrowings	0
Line of Credit Facility, Interest Rate at Period End	1.50%
Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity	$ 5,000,000