PARTNERS' CAPITAL (Series 1 Preferred Unit Purchase Agreement) (Details)	12 Months Ended
	Dec. 31, 2016
Dividend rate (in percentage)	7.50%
Period of reset related to quarterly cash contributions	5 years
Conversion price per unit (in dollars per share)	27.78
Early conversion price per unit (in dollars per share)	25.00
Distribution deferral date	Jun. 30, 2018
Optional conversion date	Jun. 01, 2018
Rating threshold at which securities are redeemable (in percentage)	50.00%