Summary of Significant Accounting Policies - Narrative (Details)	Sep. 30, 2015
Minimum
Accounting Policies [Line Items]
Percent of observatory revenue in quarter one over a ten year period	16.00%
Percent of observatory revenue in quarter two over a ten year period	26.00%
Percent of observatory revenue in quarter three over a ten year period	31.00%
Percent of observatory revenue in quarter four over a ten year period	23.00%
Maximum
Accounting Policies [Line Items]
Percent of observatory revenue in quarter one over a ten year period	18.00%
Percent of observatory revenue in quarter two over a ten year period	28.00%
Percent of observatory revenue in quarter three over a ten year period	33.00%
Percent of observatory revenue in quarter four over a ten year period	25.00%