Consolidated Statement of Changes in Capital - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year		$ 704,258
Balance at beginning of year (in shares)		26,152,976
Net income	$ 10,905	$ 23,525
Unrealized gains on available-for-sale securities		72,382
Unrealized gains on derivative financial instruments		627
Currency translation adjustments		5,484
Changes in pension liabilities and other post-retirement benefit obligations		97
Equity compensation - incentive units and vesting of restricted units		4,435
Equity compensation - subsidiaries		893
Purchases of SPLP common units		(2,985)
Purchases of subsidiary shares from noncontrolling interests		(65,589)
Other, net		1,115
Balance at end of year	$ 744,242	$ 744,242
Balance at end of period (in shares)	26,016,926	26,016,926
Total Partners' Capital
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year		$ 548,741
Net income		14,184
Unrealized gains on available-for-sale securities		71,571
Unrealized gains on derivative financial instruments		572
Currency translation adjustments		4,539
Changes in pension liabilities and other post-retirement benefit obligations		68
Equity compensation - incentive units and vesting of restricted units		4,435
Equity compensation - subsidiaries		578
Purchases of SPLP common units		(2,985)
Purchases of subsidiary shares from noncontrolling interests		21,497
Other, net		14
Balance at end of year	$ 663,214	$ 663,214
Common Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year (in shares)		36,711,663
Equity compensation - incentive units and vesting of restricted units (in shares)		23,335
Balance at end of period (in shares)	36,734,998	36,734,998
Treasury Units
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year		$ (164,900)
Balance at beginning of year (in shares)		10,558,687
Purchases of SPLP common units		$ (2,985)
Purchases of SPLP common units (in shares)		(159,385)
Balance at end of year	$ (167,885)	$ (167,885)
Balance at end of period (in shares)	10,718,072.000	10,718,072.000
Partners' Capital
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year		$ 617,502
Net income		14,184
Equity compensation - incentive units and vesting of restricted units		4,435
Equity compensation - subsidiaries		578
Purchases of SPLP common units		(2,985)
Purchases of subsidiary shares from noncontrolling interests		20,649
Other, net		14
Balance at end of year	$ 654,377	654,377
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year		(68,761)
Unrealized gains on available-for-sale securities		71,571
Unrealized gains on derivative financial instruments		572
Currency translation adjustments		4,539
Changes in pension liabilities and other post-retirement benefit obligations		68
Purchases of subsidiary shares from noncontrolling interests		848
Balance at end of year	8,837	8,837
Non-controlling interests in Consolidated Entities
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance at beginning of year		155,517
Net income		9,341
Unrealized gains on available-for-sale securities		811
Unrealized gains on derivative financial instruments		55
Currency translation adjustments		945
Changes in pension liabilities and other post-retirement benefit obligations		29
Equity compensation - subsidiaries		315
Purchases of subsidiary shares from noncontrolling interests		(87,086)
Other, net		1,101
Balance at end of year	$ 81,028	$ 81,028