Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

The following table shows the components of construction in progress.



	December 31,
(in thousands)	2017		2016

N. Glebe Road	$	83,462	$	58,147
Other	7,652		5,423
Total	$	91,114	$	63,570

Allowance for doubtful accounts

Accounts receivable in the accompanying consolidated financial statements are shown net of an allowance for doubtful accounts of $0.4 million and $2.0 million, at December 31, 2017 and 2016, respectively.



(In thousands)	Year ended December 31,
	2017			2016			2015
Beginning Balance	$	1,958		$	1,263		$	677
Provision for Credit Losses	906			1,494			915
Charge-offs	(2,459		)	(799		)	(329		)
Ending Balance	$	405		$	1,958		$	1,263

Basic and diluted shares outstanding



	December 31,
(Shares in thousands)	2017		2016		2015
Weighted average common shares outstanding - Basic	21,901		21,505		21,127
Effect of dilutive options	107		110		69
Weighted average common shares outstanding - Diluted	22,008		21,615		21,196
Average share price	$	61.63	$	58.96	$	53.38
Non-dilutive options	—		129		111
Years non-dilutive options were issued			2007, 2015, and 2016		2007 and 2015