Revenue Recognition (Tables)

3 Months Ended

Mar. 31, 2018

Revenue Recognition [Abstract]

Schedule Of Contract Liabilities From Contract With Customers

	Three Months Ended
	March 31,
	2018
Contract liabilities at beginning of period	$             14,417
Increase due to deferral of revenue	13,444
Decreases due to recognition of revenue	(12,965)
Contract liabilities at end of period	$             14,896