Revenue Recognition (Deferred Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Revenue Recognition [Abstract]
Balance at beginning of period	$ 59,915	$ 45,760
New contracts sold	9,889	8,324
Less: reductions for revenue recognized	(6,304)	(4,739)
Balance at end of period	$ 63,500	$ 49,345

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