Revenue Recognition (Deferred Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue Recognition [Abstract]
Balance at beginning of period	$ 63,500	$ 49,345	$ 59,915	$ 45,760
New contracts sold	11,496	8,848	21,385	17,172
Less: reductions for revenue recognized	(7,315)	(5,573)	(13,619)	(10,312)
Balance at end of period	$ 67,681	$ 52,620	$ 67,681	$ 52,620

Amount of deferred revenue recognized for transactions arising during the current reporting period. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an Entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

No definition available.

Name:	us-gaap_DeferredRevenueAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration