7. Intangible Assets and Liabilities

The following is a summary of intangible assets and liabilities and related accumulated amortization at June 30, 2017 and December 31, 2016:

(in thousands)	June 30, 2017			December 31, 2016
Lease intangibles:
Acquired above-market leases	$	54,609		$	45,490
Less accumulated amortization		(7,003	)		(4,940	)
Acquired above-market leases, net		47,606			40,550
Acquired in-place leases		161,830			141,676
Less accumulated amortization		(18,969	)		(14,105	)
Acquired in-place leases, net		142,861			127,571
Total intangible lease assets, net	$	190,467		$	168,121

Acquired below-market leases	$	64,413		$	54,062
Less accumulated amortization		(7,709	)		(6,191	)
Intangible lease liabilities, net	$	56,704		$	47,871

Leasing fees	$	14,822		$	13,279
Less accumulated amortization		(2,296	)		(1,950	)
Leasing fees, net	$	12,526		$	11,329

Amortization expense for acquired in-place leases and fees was $2,809 and $2,022 for the three months ended June 30, 2017 and 2016, respectively and $5,471 and $3,631 for the six months ended June 30, 2017 and 2016, respectively. Amortization of acquired above-market and below-market leases, net, was an increase (decrease) in rental income of $(188) and $150 for the three months ended June 30, 2017 and 2016, respectively and $(388) and $273 for the six months ended June 30, 2017 and 2016, respectively.

Estimated future amortization of intangible assets and liabilities at June 30, 2017 is as follows:

(in thousands)
Remainder of 2017	$	5,662
2018		11,469
2019		10,683
2020		10,574
2021		10,532
Thereafter		97,369
	$	146,289