v3.10.0.1

Subsequent Events (Details) - USD ($)																		12 Months Ended
		Feb. 14, 2019	Feb. 01, 2019	Jan. 31, 2019	Jan. 18, 2019	Nov. 14, 2018	Aug. 14, 2018	May 15, 2018	Feb. 14, 2018	Nov. 14, 2017	Aug. 14, 2017	May 15, 2017	Feb. 14, 2017	Nov. 14, 2016	Aug. 12, 2016	May 13, 2016	Feb. 12, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Debt Instrument, Face Amount																		$ 4,300,000,000	$ 4,550,000,000
Proceeds from Issuance of Senior Long-term Debt																		$ 0	$ 496,705,000	$ 1,142,997,000
Partners' Capital Account, Units, Unit-based Compensation (in shares)																		168,913	216,679	350,552
Units granted (in shares)																		302,487
Partners' Capital Account, Distribution Per Unit of Limited Partner Interest (in dollars per share)						$ 0.9775	$ 0.9575	$ 0.9375	$ 0.9200	$ 0.9050	$ 0.8900	$ 0.8725	$ 0.8550	$ 0.83750	$ 0.8200	$ 0.8025	$ 0.7850	$ 3.7925	$ 3.5225	$ 3.245
Total cash distributions						$ 223,061,000	$ 218,497,000	$ 213,933,000	$ 209,940,000	$ 206,362,000	$ 202,942,000	$ 198,951,000	$ 194,961,000	$ 190,769,000	$ 186,783,000	$ 182,797,000	$ 178,808,000	$ 865,431,000	$ 803,216,000	$ 739,157,000
6.55% Notes Due 2019 [Member]
Subsequent Event [Line Items]
Debt Instrument, Face Amount																		$ 550,000,000	$ 550,000,000
Debt Instrument, Interest Rate, Stated Percentage																		6.55%
Management [Member]
Subsequent Event [Line Items]
Partners' Capital Account, Units, Unit-based Compensation (in shares)																		168,913	216,679	350,552
Director [Member]
Subsequent Event [Line Items]
Partners' Capital Account, Units, Unit-based Compensation (in shares)	[1]																	1,691	23,961	6,117
Subsequent Event [Member]
Subsequent Event [Line Items]
Partners' Capital Account, Units, Unit-based Compensation (in shares)			208,268
Units granted (in shares)			347,473
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			3 years
Partners' Capital Account, Distribution Per Unit of Limited Partner Interest (in dollars per share)		$ 0.9975
Total cash distributions		$ 227,800,000
Subsequent Event [Member] | Four Point Two Percentage Notes Due Two Thousand Forty Five [Member]
Subsequent Event [Line Items]
Debt Instrument, Face Amount					$ 500,000,000.0
Debt Instrument, Interest Rate, Stated Percentage					4.85%
Debt Instrument, Notes At Price					99.371%
Proceeds from Issuance of Senior Long-term Debt					$ 492,500,000
Subsequent Event [Member] | Management [Member]
Subsequent Event [Line Items]
Partners' Capital Account, Units, Unit-based Compensation (in shares)			199,792
Subsequent Event [Member] | Director [Member]
Subsequent Event [Line Items]
Partners' Capital Account, Units, Unit-based Compensation (in shares)			8,476
Unionized Employees Concentration Risk [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Concentration Risk, Percentage				24.00%
Collective Bargaining Agreement, Extension Term				1 day
[1] Limited partner units issued to settle the equity-based retainer paid to independent directors of our general partner.

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