Stockholders' Equity and Non-Controlling Interests (Details)			1 Months Ended		3 Months Ended		6 Months Ended
	May 08, 2019 $ / shares	Feb. 02, 2019 $ / shares	Jun. 30, 2019 USD ($)	May 31, 2019 USD ($)	Jun. 30, 2019 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Jun. 30, 2019 USD ($) item $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Feb. 28, 2017 USD ($)
Stockholders' Equity
Dividend declared (in dollars per share) | $ / shares	$ 0.48	$ 0.48			$ 0.48	$ 0.48	$ 0.96	$ 0.96
Shares issued under ATM Agreement | shares							0	0
Authorized amount of share repurchases									$ 500,000,000.0
Common stock repurchased (in shares) | shares								573,255
Repurchase of common stock							$ 0	$ 12,090,000
Net income attributable to non-controlling interests					$ 5,430,000	$ 7,860,000	11,555,000	12,722,000
Non-controlling interest								300,000
Payment to acquire non-controlling interest							$ 30,854,000	237,551,000
2019 Notes
Stockholders' Equity
Shares issued to settle redemption | shares							3,600,000
Value of shares issued to settle redemption							$ 78,000,000.0
Convertible Senior Notes
Stockholders' Equity
Debt repurchased amount			$ 0		0		$ 0
Convertible Senior Notes | 2019 Notes
Stockholders' Equity
Shares issued to settle redemption | shares							3,600,000
Value of shares issued to settle redemption							$ 78,000,000.0
Class A Units
Stockholders' Equity
Value of shares issued to settle redemption			$ 200,000	$ 700,000
Woodstar II Portfolio | Class A Units
Stockholders' Equity
Net income attributable to non-controlling interests					$ 5,400,000	$ 4,600,000	$ 11,100,000	$ 7,100,000
Woodstar II Portfolio | Class A Units | SPT Dolphin
Stockholders' Equity
Shares issued | shares							11,900,000
Right to receive additional shares | shares							200,000
Number of common stock per unit | item							1