Subsequent Events (Details) - USD ($)	1 Months Ended	2 Months Ended	12 Months Ended
	Oct. 31, 2017	Feb. 22, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 01, 2017
Subsequent Events
Shares issued, shares	11,077
Shares issued during the period, value	$ 800,000		$ 287,437,000	$ 22,886,000	$ 83,766,000
Common Stock
Subsequent Events
Shares issued, shares			4,229,285	345,253	1,249,836
Shares issued during the period, value			$ 4,000	$ 1,000	$ 2,000
ATM
Subsequent Events
Common stock maximum offering, value			$ 84,700,000			$ 400,000,000
ATM | Common Stock
Subsequent Events
Shares issued, shares			4,229,285	345,253	1,249,836
Weighted average share price, usd per share			$ 69.03	$ 67.78	$ 68.52
Shares issued during the period, value			$ 287,500,000	$ 22,800,000	$ 84,100,000
Subsequent Event | ATM
Subsequent Events
Common stock maximum offering, value		$ 27,100,000
Subsequent Event | ATM | Common Stock
Subsequent Events
Shares issued during the period, value		$ 56,700,000
Long Term Incentive Plan | RSUs Awarded | Subsequent Event | ATM | Common Stock
Subsequent Events
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		772,858
Long Term Incentive Plan | PSUs Awarded | Subsequent Event | ATM | Common Stock
Subsequent Events
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		74.50