Acquired Intangible Assets, Net (Schedule of Acquired Intangible Assets, Net) (Details) - USD ($)
$ in Thousands |
3 Months Ended |
12 Months Ended |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
| Acquired Finite-Lived Intangible Assets [Line Items] |
|
|
|
| Acquired intangible asset, net of accumulated amortization |
$ 145,050
|
$ 154,204
|
$ 150,554
|
| Acquired intangible asset, accumulated amortization |
$ 46,578
|
$ 42,081
|
$ 22,162
|
| Acquired intangible asset, weighted average remaining life |
9 years 8 months 12 days
|
10 years 7 months 6 days
|
11 years 2 months 12 days
|
| In-place leases [Member] |
|
|
|
| Acquired Finite-Lived Intangible Assets [Line Items] |
|
|
|
| Acquired intangible asset, net of accumulated amortization |
$ 143,496
|
$ 151,135
|
$ 148,594
|
| Acquired intangible asset, accumulated amortization |
$ 45,523
|
$ 41,143
|
$ 21,776
|
| Acquired intangible asset, weighted average remaining life |
9 years 9 months 18 days
|
10 years 1 month 6 days
|
11 years
|
| Above-market leases [Member] |
|
|
|
| Acquired Finite-Lived Intangible Assets [Line Items] |
|
|
|
| Acquired intangible asset, net of accumulated amortization |
$ 1,554
|
$ 1,710
|
$ 1,344
|
| Acquired intangible asset, accumulated amortization |
$ 1,055
|
$ 899
|
$ 358
|
| Acquired intangible asset, weighted average remaining life |
4 years 9 months 18 days
|
5 years 1 month 6 days
|
2 years 9 months 18 days
|
| Ground lease assets [Member] |
|
|
|
| Acquired Finite-Lived Intangible Assets [Line Items] |
|
|
|
| Acquired intangible asset, net of accumulated amortization |
|
$ 1,359
|
$ 616
|
| Acquired intangible asset, accumulated amortization |
|
$ 39
|
$ 28
|
| Acquired intangible asset, weighted average remaining life |
|
83 years 6 months
|
65 years 9 months 18 days
|