Summary of Significant Accounting Principles (Details-2) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities	$ 91,618,000	$ 67,016,000
Cash used for investing activities	(103,071,000)	(46,874,000)
Change in cash, cash equivalents, and restricted cash	(11,827,000)	6,337,000
Cash, cash equivalents, and restricted cash at beginning of period	112,094,000	101,633,000
Cash, cash equivalents, and restricted cash at end of period	$ 100,267,000	107,970,000
Accounting Standards Update 2016-18 - Restricted Cash [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities		(694,000)
Cash used for investing activities		74,000
Change in cash, cash equivalents, and restricted cash		(620,000)
Cash, cash equivalents, and restricted cash at beginning of period		5,674,000
Cash, cash equivalents, and restricted cash at end of period		$ 5,054,000