Geographic Concentrations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 415,817	$ 402,010	$ 394,667	$ 391,141	$ 401,721	$ 389,501	$ 379,451	$ 372,914	$ 1,603,635	$ 1,543,587	$ 1,489,999
Total Assets	2,532,428				2,394,897				2,532,428	2,394,897
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									1,313,811	1,253,879	1,212,799
Total Assets	2,242,078				2,078,187				2,242,078	2,078,187
Australia
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									227,374	219,738	207,035
Total Assets	226,666				244,841				226,666	244,841
New Zealand
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									32,363	33,289	33,676
Total Assets	51,419				54,672				51,419	54,672
Argentina
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									11,752	18,319	19,780
Total Assets	7,154				11,598				7,154	11,598
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues									18,335	18,362	$ 16,709
Total Assets	$ 5,111				$ 5,599				$ 5,111	$ 5,599