The cumulative difference between the rental payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense over the term of the leased property by the lessor or lessee, respectively.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Leases - Narrative (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred Rent Credit		$ 600,000
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			$ (995,000)
Other Assets [Member]
Operating Lease, Right-of-Use Asset	$ 10,600,000	11,000,000.0
Other Liabilities [Member]
Operating Lease, Liability	$ 11,388,000	11,800,000
Adjustments for Change in Accounting Principle [Domain] \| Retained Earnings [Member]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		$ 143,000