Shareholders' Equity - Treasury Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended	20 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2018	Nov. 14, 2016	May 02, 2012
Equity [Abstract]
Number of shares authorized to be repurchased (in shares)				500,000.0	500,000
Number of shares repurchased (in shares)	13,879	13,879	65,915
Payments for repurchase of common stock			$ 0.3
Remaining number of shares authorized to be repurchased (in shares)	434,085	434,085	434,085
Average price per share of treasury stock acquired (in dollars per share)		$ 45.95
Movement in Treasury Stock [Roll Forward]
Beginning balance (in shares)		633,939
Purchases (in shares)	13,879	13,879	65,915
Restricted stock grants (in shares)		(160,146)
Forfeitures and other (in shares)		46,838
Ending balance (in shares)	534,510	534,510	534,510