Consolidated Statement of Changes in Capital (unaudited) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year (in shares)			25,023,128				25,023,128
Balance at beginning of year	$ 429,289	$ 429,519	$ 476,419	$ 522,411	$ 503,394	$ 492,508	$ 476,419	$ 492,508
Net income (loss)	38,523	(1,677)	(61,607)	(2,764)	21,034	15,622	$ (24,761)	33,892
Currency translation adjustments	1,379	1,373	(2,936)	(2,401)	(1,797)	1,303
Equity compensation - restricted units	334	49	104	243	227	164
Deconsolidation of API (see Note 3)			17,481
Other, net	$ 65	25	58	123	(22)
Unrealized gains on derivative financial instruments				71	(425)	518
Purchases of SPLP common units						(6,721)
Balance at end of period (in shares)	25,189,613						25,189,613
Balance at end of year	$ 469,590	429,289	429,519	517,683	522,411	503,394	$ 469,590	517,683
Total Partners' Capital
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year	425,074	425,523	472,613	518,775	499,729	488,787	472,613	488,787
Net income (loss)	38,275	(1,868)	(61,737)	(2,878)	21,063	15,678
Currency translation adjustments	1,379	1,373	(2,936)	(2,401)	(1,797)	1,303
Equity compensation - restricted units	334	49	104	243	227	164
Deconsolidation of API (see Note 3)			17,481
Other, net	(1)	(3)	(2)	123	(22)
Unrealized gains on derivative financial instruments				71	(425)	518
Purchases of SPLP common units						(6,721)
Balance at end of year	$ 465,061	$ 425,074	$ 425,523	$ 513,933	$ 518,775	$ 499,729	$ 465,061	$ 513,933
Common Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year (in shares)	37,577,117	37,661,138	37,670,992	37,659,006	37,606,531	37,436,531	37,670,992	37,436,531
Equity compensation - restricted units (in shares)	260,360	(84,021)	(9,854)	0	52,475	170,000
Balance at end of period (in shares)	37,837,477	37,577,117	37,661,138	37,659,006	37,659,006	37,606,531	37,837,477	37,659,006
Treasury Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year (in shares)	12,647,864	12,647,864	12,647,864	12,647,864	12,647,864	12,142,528	12,647,864	12,142,528
Balance at beginning of year	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)	$ (192,060)	$ (198,781)	$ (192,060)
Purchases of SPLP common units (in shares)						(505,336)
Purchases of SPLP common units						$ (6,721)
Balance at end of period (in shares)	12,647,864	12,647,864	12,647,864	12,647,864	12,647,864	12,647,864	12,647,864	12,647,864
Balance at end of year	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)	$ (198,781)
Partners' Capital
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year	600,578	602,400	664,035	696,420	675,152	666,031	664,035	666,031
Net income (loss)	38,275	(1,868)	(61,737)	(2,878)	21,063	15,678
Equity compensation - restricted units	334	49	104	243	227	164
Other, net	(1)	(3)	(2)	123	(22)
Purchases of SPLP common units						(6,721)
Balance at end of year	639,186	600,578	602,400	693,908	696,420	675,152	639,186	693,908
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year	(175,504)	(176,877)	(191,422)	(177,645)	(175,423)	(177,244)	(191,422)	(177,244)
Currency translation adjustments	1,379	1,373	(2,936)	(2,401)	(1,797)	1,303
Deconsolidation of API (see Note 3)			17,481
Unrealized gains on derivative financial instruments				71	(425)	518
Balance at end of year	(174,125)	(175,504)	(176,877)	(179,975)	(177,645)	(175,423)	(174,125)	(179,975)
Noncontrolling Interests in Consolidated Entities
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year	4,215	3,996	3,806	3,636	3,665	3,721	3,806	3,721
Net income (loss)	248	191	130	114	(29)	(56)
Other, net	66	28	60
Balance at end of year	$ 4,529	$ 4,215	$ 3,996	$ 3,750	$ 3,636	$ 3,665	$ 4,529	$ 3,750