Long Term Debt (Details) $ in Thousands		3 Months Ended
	Jun. 04, 2014 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Long Term Debt
Notes payable - WEST II		$ 852,156	$ 840,956
Notes payable Member
Long Term Debt
Interest rate, minimum (as a percent)		2.40%
Interest rate, maximum (as a percent)		5.50%
Notes payable Member | Minimum
Long Term Debt
Maturity term		2 years 3 months 18 days
Notes payable Member | Maximum
Long Term Debt
Maturity term		8 years 9 months 18 days
Revolving credit facility
Long Term Debt
Maximum borrowing capacity under credit facility	$ 700,000
Maximum borrowing capacity under credit facility before amendment	$ 450,000
Extended maturity term	5 years
Debt issuance costs	$ 4,900
Remaining borrowing capacity available		$ 183,000	$ 270,000
Leverage ratio			4.25
Variable rate of debt		one-month LIBOR
Basis spread on variable rate (as a percent)		2.75%