(4)	Goodwill and Other Intangible Assets

Goodwill was $74.6 million and $11.3 million as of December 31, 2015 and 2014, respectively. There were no impairments recorded against goodwill in 2015, 2014 or 2013. The following table displays the changes in the gross carrying amount of goodwill:

 

		Amount
		(in thousands)
Balance at December 31, 2014 and 2013			11,265
NTO acquisition			4,590
Logentries acquisition			58,710
Balance at December 31, 2015			$74,565

Identifiable intangible assets consist of the following:

 

						As of December 31, 2015												As of December 31, 2014
		Weighted- Average Life (years)				Gross Carrying Amount				Accumulated Amortization				Net Book Value				Gross Carrying Amount				Accumulated Amortization				Net Book Value
						(in thousands)
Intangible assets subject to amortization:
Developed technology			5.9				$12,851				$(2,955)				$9,896				$2,601				$(1,934)				$667
Trade names			6.3				719				(389)				330				494				(280)				214
Customer relationships			6.7				1,000				(43)				957				—				—				—
Non-compete agreements			4.8				540				(338)				202				500				(225)				275
Total intangible assets							$15,110				$(3,725)				$11,385				$3,595				$(2,439)				$1,156

Amortization of intangible assets is expensed on a straight-line basis over the useful life of the asset. We recorded amortization expense of $1.3 million, $0.9 million and $0.9 million in 2015, 2014 and 2013, respectively.

Estimated future amortization expense of the acquired identifiable intangible assets as of December 31, 2015 is as follows (in thousands):

 

2016		$	2,285
2017			2,034
2018			1,915
2019			1,880
2020			1,837
2021 and thereafter			1,434
Total		$	11,385