Intangible Assets and Deferred Credits

For the years ended December 31, 2011 and 2010, the Company recorded $23.4 million and $39.1 million, respectively, of site rental contracts and customer relationships. The following is a summary of the Company's intangible assets.



	As of December 31, 2011							As of December 31, 2010
	Gross Carrying Value		Accumulated Amortization			Net Book Value		Gross Carrying Value		Accumulated Amortization			Net Book Value
Site rental contracts and customer relationships	$	2,823,832	$	(748,850	)	$	2,074,982	$	2,799,804	$	(602,426	)	$	2,197,378
Other intangible assets	152,375		(49,175		)	103,200		150,558		(34,007		)	116,551
Total	$	2,976,207	$	(798,025	)	$	2,178,182	$	2,950,362	$	(636,433	)	$	2,313,929

Amortization expense related to intangible assets is classified as follows on the Company's consolidated statement of operations and comprehensive income (loss):



	For Years Ended December 31,
Classification	2011		2010		2009
Depreciation, amortization and accretion	$	159,478	$	156,150	$	145,192
Site rental costs of operations	3,709		3,764		4,051
Total amortization expense	$	163,187	$	159,914	$	149,243

The estimated annual amortization expense related to intangible assets (inclusive of those recorded to "site rental costs of operations") for the years ended December 31, 2012 to 2016 is as follows:



	Years Ending December 31,
	2012		2013		2014		2015		2016
Estimated annual amortization	$	159,509	$	151,288	$	145,761	$	140,146	$	140,139

See note 2 for a further discussion of deferred credits related to above-market leases for land interests under the Company's towers recorded in connection with acquisitions. For the years ended December 31, 2011, 2010 and 2009, the Company recorded $3.8 million, $4.4 million and $4.5 million, respectively, as a decrease to "site rental costs of operations." The following is a summary of the Company's above-market leases.



	As of December 31, 2011							As of December 31, 2010
	Gross Carrying Value		Accumulated Amortization			Net Book Value		Gross Carrying Value		Accumulated Amortization			Net Book Value
Above-market leases	$	67,132	$	(17,816	)	$	49,316	$	70,331	$	(17,669	)	$	52,662

The estimated annual amortization expense related to above-market leases for land interests under the Company's towers for the years ended December 31, 2012 to 2016 is as follows:



	Years Ending December 31,
	2012		2013		2014		2015		2016
Estimated annual amortization	$	3,504	$	3,434	$	3,410	$	3,386	$	3,469