Note 13. Revenues

Rents for 2015, 2014 and 2013, respectively, are comprised of the following:


	Years ended December 31,
	2015	2014	2013
Base rents	$ 112,319,000	$ 110,739,000	$ 103,721,000
Percentage rent	789,000	683,000	804,000
Straight-line rents	506,000	761,000	1,387,000
Amortization of intangible lease liabilities, net	3,125,000	4,322,000	4,441,000
Total rents	$ 116,739,000	$ 116,505,000	$ 110,353,000

Annual future base rents due to be received under non-cancelable operating leases in effect at December 31, 2015 are approximately as follows (excluding those base rents applicable to properties classified as real estate held for sale):


2016		$ 108,891,000
2017		99,195,000
2018		89,025,000
2019		74,704,000
2020		57,484,000
Thereafter		250,979,000
		$ 680,278,000

Total future minimum rents do not include expense recoveries for real estate taxes and operating costs, or percentage rents based upon tenants’ sales volume. Such additional revenue amounts aggregated approximately $32.6 million, $32.1 million and $29.5 million for 2015, 2014 and 2013, respectively. Such amounts do not include amortization of intangible lease liabilities.