Debt - Cash Pool (Details) $ in Thousands	Sep. 30, 2019 USD ($) cash_pool	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Number of cash pools | cash_pool	2
QRS Cash Pool
Debt Instrument [Line Items]
Number of cash pools | cash_pool	1
Gross Cash Position	$ 358,200	$ 300,800
Outstanding Debit Balances	(355,800)	(298,800)
Net Cash Position	$ 2,400	2,000
TRS Cash Pool
Debt Instrument [Line Items]
Number of cash pools | cash_pool	1
Gross Cash Position	$ 302,200	281,500
Outstanding Debit Balances	(296,300)	(279,300)
Net Cash Position	$ 5,900	$ 2,200