3.	PROPERTY AND EQUIPMENT, NET

Property and equipment and accumulated depreciation and amortization were as follows:

	June 30,			December 31,
	2017			2016
Property and equipment
Buildings	$	60,095		$	48,250
Software and capitalized software costs		30,771			23,879
Computer equipment		23,073			18,987
Rental clocks		11,723			10,669
Furniture, fixtures and equipment		7,052			6,695
Leasehold improvements		715			680
		133,429			109,160
Less: accumulated depreciation and amortization		(43,706	)		(35,833	)
		89,723			73,327
Construction in progress		18,241			14,528
Land		8,993			8,993
Property and equipment, net	$	116,957		$	96,848

We capitalize computer software development costs related to software developed for internal use in accordance with Accounting Standards Codification (“ASC”) Topic 350-40. For the three and six months ended June 30, 2017, we capitalized $3.5 million and $6.4 million, respectively, of computer software development costs related to software developed for internal use. For the three and six months ended June 30, 2016, we capitalized $2.0 million and $3.7 million, respectively, of computer software development costs related to software developed for internal use.

Rental clocks included in property and equipment, net represent time clocks issued to clients under month-to-month operating leases. As such, these items are transferred from inventory to property and equipment and depreciated over their useful estimated lives.

Included in the construction in progress balance at June 30, 2017 and December 31, 2016 is $1.2 million and $1.1 million in retainage, respectively.

We capitalize interest incurred for indebtedness related to construction of our principal executive offices. For the three and six months ended June 30, 2017, we incurred interest costs of $0.4 million and $0.8 million, respectively, of which we capitalized $0.1 million and $0.2 million, respectively. For the three and six months ended June 30, 2016, we incurred interest costs of $0.2 million and $0.5 million, respectively, of which we capitalized $0.2 million and $0.2 million, respectively.

Depreciation and amortization expense for property and equipment, net was $4.3 million and $8.2 million, respectively, for the three and six months ended June 30, 2017. Depreciation and amortization expense for property and equipment, net was $2.8 million and $5.3 million, respectively, for the three and six months ended June 30, 2016.