Stockholders' Equity Share Repurchases (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($) shares	Sep. 30, 2017 USD ($) shares
Equity [Abstract]
Stock repurchased during period (in shares) | shares	0	145,786
Stock repurchased during period, value	$ 0.0	$ 10.0
Cumulative amount of shares repurchased (in shares) | shares	1,000,657	1,000,657
Cumulative payments for repurchase of common stock	$ 82.9	$ 82.9
Remaining dollar value of shares that may be repurchased	$ 67.1	$ 67.1