Debt and Capital Lease Obligations (Details) (USD $)					9 Months Ended				9 Months Ended					12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Senior Notes [Member]	Dec. 31, 2013 Senior Notes [Member]	Sep. 30, 2014 Line of Credit [Member]	Dec. 31, 2013 Line of Credit [Member]	Sep. 30, 2014 Capital Lease Obligations [Member]	Dec. 31, 2013 Capital Lease Obligations [Member]	Sep. 30, 2014 Senior Notes Series A [Member]	Sep. 30, 2014 Senior Notes Series B [Member]	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Maximum [Member]	Dec. 31, 2014 Interest Rate Swap [Member]	Dec. 31, 2014 Interest Rate Swap No. 1 [Member]	Dec. 31, 2014 Interest Rate Swap No. 2 [Member]
Debt Instrument [Line Items]
Total debt	$ 370,005,000	$ 267,028,000	$ 150,000,000	$ 150,000,000	$ 220,000,000	$ 117,000,000	$ 5,000	$ 28,000
Less - current maturities of long-term debt and capital lease obligations	5,000	26,000
Long-term debt and capital lease obligations, net	370,000,000	267,002,000
Face amount			150,000,000						75,000,000	75,000,000
Maturity date					Aug. 29, 2019				Sep. 30, 2021	Sep. 30, 2023
Interest rate, effective percentage									4.01%	4.11%
Line of credit facility, current borrowing capacity	350,000,000
Line of credit facility, maximum borrowing capacity	400,000,000
Debt instrument, basis spread on variable rate											1.25%	2.00%
Performance bonds under credit facility	25,500,000
Line of credit facility, remaining borrowing capacity	104,500,000
Performance bonds	19,500,000
Derivative, Amount of Hedged Item													50,000,000
Derivative, Notional Amount													$ 50,000,000	$ 25,000,000	$ 25,000,000
Derivative, Maturity Date														Aug. 29, 2024	Aug. 29, 2019
Derivative, Fixed Interest Rate														2.50%	1.73%
Derivative, Fixed Rate and Debt Instrument, Basis Spread on Variable Rate														3.75%	2.98%