Intangible Assets

The following table summarizes the components of our intangible assets at the dates indicated:



	March 31, 2018						December 31, 2017
	Gross Carrying Amount		Accumulated Amortization		Carrying Value		Gross Carrying Amount		Accumulated Amortization		Carrying Value
Sodium minerals and sulfur services:
Customer relationships	$	94,654	$	93,033	$	1,621	$	94,654	$	92,493	$	2,161
Licensing agreements	38,678		37,066		1,612		38,678		36,528		2,150
Non-compete agreement	800		156		644		800		89		711
Segment total	134,132		130,255		3,877		134,132		129,110		5,022
Onshore Facilities & Transportation:
Customer relationships	35,430		35,093		337		35,430		35,082		348
Intangibles associated with lease	13,260		5,051		8,209		13,260		4,933		8,327
Segment total	48,690		40,144		8,546		48,690		40,015		8,675
Marine contract intangibles	27,000		13,050		13,950		27,000		11,700		15,300
Offshore pipeline contract intangibles	158,101		22,190		135,911		158,101		20,109		137,992
Other	30,684		14,213		16,471		28,900		13,483		15,417
Total	$	398,607	$	219,852	$	178,755	$	396,823	$	214,417	$	182,406

Our amortization of intangible assets for the periods presented was as follows:



	Three Months Ended March 31,
	2018		2017
Amortization of intangible assets	$	5,433	$	5,872

We estimate that our amortization expense for the next five years will be as follows: