Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Sep. 30, 2018	May 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Proceeds From Issuance Of Common Stock			$ 57,845	$ (93)
Preferred stock, par value (in dollars per share)			$ 0.0001		$ 0.0001
Preferred stock, shares authorized			4,000,000		4,000,000
Series A Junior Participating Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Redesignated of Shares Authorized			200,000
Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues			874,268
Common Stock [Member] | Forward Sale Agreement [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	3,500,000
At-Market Equity Program [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues			874,268		3,057,263
Proceeds From Issuance Of Common Stock			$ 58,400
Gross Amount Remaining To Be Issued			$ 10,400
Value Of Equity Instruments To Be Issued		$ 250,000
Common stock Average Price			$ 66.79
September 2018 Forward Sales [Member]
Class of Stock [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Date	Sep. 03, 2019