Shareholders' Equity - Narrative (Details) - USD ($)			1 Months Ended	3 Months Ended
	Mar. 14, 2018	Mar. 15, 2017	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Class of Stock [Line Items]
Stock repurchase program, period in force	12 months
Common Shares
Class of Stock [Line Items]
Stock repurchase program, authorized amount (up to)		$ 150,000,000
Stock repurchase program, period in force		12 months
Stock repurchase program, amount not utilized			$ 81,000,000
Stock repurchase program, additional authorized amount (up to)	$ 150,000,000
Stock repurchased and retired during period (in shares)				2,970,209
Stock repurchased and retired during period, price per share (in dollars per share)				$ 29.67
Stock repurchased and retired during period, value	$ 19,100,000	$ 69,000,000		$ 88,100,000
Stock repurchase program, remaining authorized repurchase amount			$ 130,900,000	$ 130,900,000
Number of shares surrendered to satisfy tax withholding obligations (in shares)				57,348	6,694