Capital Stock and Share Based Compensation Plans - Narrative (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended
	Dec. 31, 2014 common_share director	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Nov. 30, 2012
Class of Stock [Line Items]
Classes of common shares	2			2
Minimum number of directors up for election to entitle shareholders to vote	3			3
Minumum percent of directors up for election to entitle shareholders to vote	33.33%			33.33%
Stock repurchased during period, value	$ 21,237,000	$ 74,199,000	$ 23,564,000
Number of shares available for future stock compensation grants	4,200,000.0			4,200,000.0
Total unrecognized compensation cost related to restricted stock, RSUs and performance shares	5,200,000			5,200,000
Stock Options | Common stock, Class A | Maximum
Class of Stock [Line Items]
Purchase price of stock options granted, percent of fair market value	100.00%
Restricted Stock and Restricted Stock Units | Minimum
Class of Stock [Line Items]
Vesting period of stock options	3 years
Restricted Stock and Restricted Stock Units | Maximum
Class of Stock [Line Items]
Vesting period of stock options	4 years
Restricted Stock Units (RSUs) [Member]
Class of Stock [Line Items]
Weighted-average period of recognition, years	1 year 6 months
First Repurchase Plan | Minimum
Class of Stock [Line Items]
Range of price of shares repurchased	$ 10.83
First Repurchase Plan | Maximum
Class of Stock [Line Items]
Range of price of shares repurchased	$ 19.99
First Repurchase Plan | Common stock, Class A
Class of Stock [Line Items]
Stock repurchase program, authorized amount					100,000,000
Stock repurchased during period, value	95,000,000
Stock repurchase program, remaining authorized repurchase amount				0
Second Repurchase Plan [Member] | Common stock, Class A
Class of Stock [Line Items]
Stock repurchase program, authorized amount	100,000,000
Stock repurchased during period, value	$ 0