Shareholders' Equity Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended
	Jul. 02, 2018	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	May 07, 2018
Class of Stock [Line Items]
Net cash proceeds of common stock			$ 22,492	$ 17,390
At The Market Equity Program
Class of Stock [Line Items]
Aggregate offering price of common share					$ 400,000
Shares sold		199,263	199,263
Weighted average price per common share		$ 125.46	$ 125.46
Net cash proceeds of common stock		$ 24,600	$ 24,600
Remaining capacity to issue		375,000	375,000
At The Market Equity Program | Subsequent Event
Class of Stock [Line Items]
Common shares sold prior to the period end, but subsequently settled	50,700
At The Market Equity Program | Commissions
Class of Stock [Line Items]
Commissions related to sales of common shares		300	300
At The Market Equity Program | Other offering costs
Class of Stock [Line Items]
Commissions related to sales of common shares		$ 100	$ 100