Shareholders' Equity - Share Repurchases/Sale of Shares (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended								12 Months Ended
	Jan. 16, 2020	Aug. 03, 2017	Jul. 05, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Share repurchases (in shares)												15,588	4,984	3,590
Stock repurchase price (in dollars per share)												$ 29.76	$ 46.54	$ 73.63
Common distributions declared (in dollars per share)				$ 0.55	$ 0.55	$ 0.55	$ 0.55	$ 1.72	$ 1.72	$ 1.72	$ 1.72
Sale of stock, consideration received on transaction		$ 493,866
Underwritten Public Offering
Class of Stock [Line Items]
Number of shares sold (in shares)			6,250,000
Sale of stock (in dollars per share)			$ 74.00
Over-Allotment Option
Class of Stock [Line Items]
Number of shares sold (in shares)		726,757
Sale of stock (in dollars per share)		$ 74.00
Subsequent Event
Class of Stock [Line Items]
Common distributions declared (in dollars per share)	$ 0.55
Dividends payable	$ 26,511