Long-Term Debt and Capital Leases (Details) (USD $)	3 Months Ended							3 Months Ended				3 Months Ended										3 Months Ended			0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Redemption of Notes [Member]	May 24, 2012 Redemption of Notes [Member]	Mar. 28, 2013 Maximum [Member]	Mar. 27, 2013 Maximum [Member]	Mar. 31, 2013 Revolving Loan Facility [Member]	Dec. 31, 2012 Revolving Loan Facility [Member]	Mar. 31, 2013 Senior Notes [Member]	Dec. 31, 2012 Senior Notes [Member]	Mar. 31, 2013 Note Payable to Banks [Member]		Dec. 31, 2012 Note Payable to Banks [Member]	Mar. 31, 2013 Capital Lease Obligations [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Mar. 31, 2013 LIBOR [Member]	Mar. 31, 2013 LIBOR [Member] Maximum [Member]	Mar. 31, 2013 LIBOR [Member] Minimum [Member]	Mar. 31, 2013 Prime Rate [Member] Maximum [Member]	Mar. 31, 2013 Prime Rate [Member] Minimum [Member]	Mar. 31, 2013 Senior Notes 8.875% [Member] Senior Notes [Member]		Dec. 31, 2012 Senior Notes 8.875% [Member] Senior Notes [Member]	Feb. 11, 2013 Senior Notes 7.250% [Member] Senior Notes [Member]	Mar. 31, 2013 Senior Notes 7.250% [Member] Senior Notes [Member]	Dec. 31, 2012 Senior Notes 7.250% [Member] Senior Notes [Member]	May 06, 2013 Subsequent Event [Member]	Apr. 02, 2013 Subsequent Event [Member] LIBOR [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	The applicable margin for revolving loans that are LIBOR loans ranges from 2.00% to 3.25% and the applicable margin for revolving loans that are base prime rate loans ranges from 1.00% to 2.25%.  The applicable margin for existing LIBOR borrowings is 3.00%.  Effective October 1, 2012, the applicable margin for existing LIBOR borrowings remained at 3.00%.  Effective January 1, 2013, the applicable margin for existing LIBOR borrowings will decrease to 2.25%.
Total long-term debt and capital lease obligations	$ 523,193,000		$ 478,198,000					$ 91,000,000	$ 296,000,000			$ 2,939,000		$ 2,971,000	$ 5,789,000	$ 5,839,000						$ 173,465,000		$ 173,388,000		$ 250,000,000	$ 0
Less current installments	3,192,000		3,206,000
Long-term debt and capital lease obligations, net of current installments	520,001,000		474,992,000
Applicable margins																	2.50%	3.00%	2.00%	2.00%	1.00%								2.50%
Applicable margin for next three months																	2.50%
Face amount								600,000,000				7,354,000										200,000,000	[1]		250,000,000
Unamortized discount										1,535,000	1,612,000
Weighted average interest rate								3.72%																				3.02%
Stated interest rate												4.75%	[2]									8.875%			7.25%
Maturity date								Apr. 30, 2016				Jan. 31, 2017										Apr. 30, 2018			Feb. 28, 2021
Partnership redemption option maximum				35.00%
Partnership senior note redemption option price				108.875%
Partnership redemption of the senior notes					25,000,000
Maximum amount of borrowings and letters of credit available under Credit Facility						600,000,000	400,000,000
Cash paid for interest	2,217,000	2,408,000
Capitalized interest	$ 180,000	$ 353,000

[1] Pursuant to the Indenture under which the Senior Notes due in 2018 were issued, the Partnership has the option to redeem up to 35% of the aggregate principal amount at a redemption price of 108.875% of the principal amount, plus accrued and unpaid interest with the proceeds of certain equity offerings. On April 24, 2012, the Partnership notified the Trustee of its intention to exercise a partial redemption of the Partnership’s Senior Notes pursuant to the Indenture. On May 24, 2012, the Partnership redeemed $25,000 of the Senior Notes from various holders using proceeds of the Partnership’s January 2012 follow-on equity offering, which in the interim were used to pay down amounts outstanding under the Partnership’s revolving credit facility.

[2] Interest rate fluctuates based on the LIBOR rate plus an applicable margin set on the date of each advance. The margin above LIBOR is set every three months. Indebtedness under the credit facility bears interest at LIBOR plus an applicable margin or the base prime rate plus an applicable margin. The applicable margin for revolving loans that are LIBOR loans ranges from 2.00% to 3.00% and the applicable margin for revolving loans that are base prime rate loans ranges from 1.00% to 2.00%. The applicable margin for existing LIBOR borrowings is 2.50%. Effective April 1, 2013, the applicable margin for existing LIBOR borrowings remained at 2.50%. Effective July 1, 2013, the applicable margin for existing LIBOR borrowings will remain at 2.50%. As of May 6, 2013, our weighted average interest rate on our revolving loan facility is 3.02%.