Shareholders' Equity (Narrative) (Details) $ / shares in Units, $ in Millions									12 Months Ended			67 Months Ended	110 Months Ended	126 Months Ended
	Oct. 29, 2015 $ / shares	May. 19, 2015 $ / shares shares	Nov. 04, 2014 $ / shares	Jul. 16, 2014	May. 02, 2014 $ / shares	Nov. 06, 2013 $ / shares	Jul. 02, 2013	May. 21, 2013 $ / shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Oct. 31, 2015 USD ($)	May. 18, 2015 shares
Schedule of Shareholders' Equity [Line Items]
Dividends declared (per share) | $ / shares									$ 0.22	$ 0.18	$ 0.13
Stock split, conversion ratio				1.5			1.5
Cash dividends paid | $									$ 11.9	$ 9.7	$ 7.4
Regular Semi-Annual Dividend
Schedule of Shareholders' Equity [Line Items]
Dividends declared (per share) | $ / shares	$ 0.11	$ 0.11	$ 0.09		$ 0.09	$ 0.07		$ 0.06
2010 Stock Repurchase Program
Schedule of Shareholders' Equity [Line Items]
Stock repurchase program authorized percentage												5.00%
Stock repurchase program amount authorized (in shares) | shares									2,900,000			2,900,000	2,900,000	2,900,000
Stock repurchase program amount authorized, value | $															$ 25.0
Stock repurchased during period (in shares) | shares									1,000,000	1,000,000		3,700,000
Aggregate price of shares repurchased since inception | $												$ 56.5
Average price of shares repurchased since inception (per share) | $ / shares												$ 15.40
2010 Stock Repurchase Program [Member]
Schedule of Shareholders' Equity [Line Items]
Stock repurchase program amount authorized (in shares) | shares		5,700,000														2,750,000.00
2005 401(k) Stock Repurchase Program
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares) | shares														5,500,000
Aggregate price of shares repurchased since inception | $														$ 50.9
Average price of shares repurchased since inception (per share) | $ / shares														$ 9.18
2006 Director and Officer Repurchase Program
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares) | shares													1,800,000
Aggregate price of shares repurchased since inception | $													$ 14.8
Average price of shares repurchased since inception (per share) | $ / shares													$ 8.05