Capital and Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of year	$ 801,460	$ 669,048
Net other comprehensive income (loss) attributable to common unitholders	1,093	(459)
Balance at end of year	819,841	654,225
Unrealized loss on available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of year	(92)	(92)
Net other comprehensive income (loss) attributable to common unitholders	0	0
Balance at end of year	(92)	(92)
Cumulative translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of year	(17,113)	(13,961)
Net other comprehensive income (loss) attributable to common unitholders	1,093	(459)
Balance at end of year	(16,020)	(14,420)
Change in net pension and other benefit obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of year	(134,669)	(117,750)
Net other comprehensive income (loss) attributable to common unitholders	0	0
Balance at end of year	(134,669)	(117,750)
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of year	(151,874)	(131,803)
Net other comprehensive income (loss) attributable to common unitholders	1,093	(459)
Balance at end of year	$ (150,781)	$ (132,262)