CONSOLIDATED AND CONDENSED STATEMENTS OF CAPITAL (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance	$ 260,417	$ 357,962
Net income	11,795	16,637
Issuance of common units	5,235
General partner contribution	114	37
Cash distributions	(21,370)	(20,957)
Unit-based compensation	179	256
Purchase of treasury units	(277)
Ending Balance	256,093	353,935
Limited Partner [Member] | Common Limited [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance (in units)	26,625,026	26,566,776
Beginning Balance	254,028	349,490
Net income	11,559	16,304
Issuance of common units (in units)	132,580
Issuance of common units	5,235
Issuance of restricted units (in units)	6,400	57,750
Forfeiture of restricted units (in units)	(2,750)
Cash distributions	(20,898)	(20,501)
Unit-based compensation	179	256
Purchase of treasury units (in units)	(6,400)
Purchase of treasury units	(277)
Ending Balance (in units)	26,754,856	26,624,526
Ending Balance	249,826	345,549
General Partner [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance	6,389	8,472
Net income	236	333
General partner contribution	114	37
Cash distributions	(472)	(456)
Ending Balance	$ 6,267	$ 8,386