Acquired Intangible Assets and Liabilities

The following summarizes our acquired intangible assets (real estate intangibles, comprised of acquired in place lease value, tenant relationship value and trade name along with acquired above-market lease value) and intangible liabilities (acquired below-market lease value) as of December 31, 2015 and 2014.



	Balance as of
(Amounts in thousands)	December 31, 2015			December 31, 2014
Real Estate Intangibles:
Acquired in place lease value:
Gross amount	$	901,381		$	680,419
Accumulated amortization	(472,933		)	(452,739		)
Net	$	428,448		$	227,680
Tenant relationship value:
Gross amount	$	734,800		$	—
Accumulated amortization	(14,495		)	—
Net	$	720,305		$	—
Trade name:
Gross amount	$	7,300		$	—
Accumulated amortization	(417		)	—
Net	$	6,883		$	—
Acquired above market leases:
Gross amount	$	122,311		$	126,677
Accumulated amortization	(89,613		)	(88,072		)
Net	$	32,698		$	38,605
Acquired below market leases:
Gross amount	$	294,791		$	282,670
Accumulated amortization	(193,677		)	(178,435		)
Net	$	101,114		$	104,235

Amortization of acquired below-market lease value, net of acquired above-market lease value, resulted in an increase to rental revenues of $9.3 million, $10.0 million and $11.7 million for the years ended December 31, 2015 , 2014 and 2013, respectively. The expected average remaining lives for acquired below market leases and acquired above market leases is 5.9 years and 3.7 years, respectively, as of December 31, 2015. Estimated annual amortization of acquired below-market lease value, net of acquired above-market lease value, for each of the five succeeding years and thereafter, commencing January 1, 2016 is as follows:



(Amounts in thousands)
2016	$	8,403
2017	6,867
2018	5,222
2019	5,285
2020	7,351
Thereafter	35,288
Total	$	68,416

Amortization of acquired in place lease value (a component of depreciation and amortization expense) was $46.2 million, $62.2 million and $62.7 million for the years ended December 31, 2015, 2013 and 2012, respectively. The expected average amortization period for acquired in place lease value is 6.3 years as of December 31, 2015. The weighted average remaining contractual life for acquired leases excluding renewals or extensions is 4.9 years as of December 31, 2015. Estimated annual amortization of acquired in place lease value for each of the five succeeding years and thereafter, commencing January 1, 2016 is as follows:



(Amounts in thousands)
2016	$	53,391
2017	48,879
2018	46,636
2019	44,150
2020	40,108
Thereafter	195,284
Total	$	428,448

Amortization of tenant relationship value and trade names (a component of depreciation and amortization expense) was approximately $14.5 million and $0.4 million, respectively for the year ended December 31, 2015 and $0 in all preceding years. The weighted average remaining contractual life for customer contracts and trade names is 11.4 years and 3.8 years, respectively. Estimated annual amortization of customer contracts and trade names for each of the five succeeding years and thereafter, commencing January 1, 2016 is as follows:



(Amounts in thousands)
2016	$	65,261
2017	65,261
2018	65,261
2019	64,844
2020	63,436
Thereafter	403,125
Total	$	727,188