Capital Stock - Narrative (Details) (USD $)	3 Months Ended								1 Months Ended	0 Months Ended
	Mar. 31, 2014 common_share director	Mar. 31, 2013	Mar. 31, 2014 Minimum	Mar. 31, 2013 Minimum	Mar. 31, 2014 Maximum	Mar. 31, 2013 Maximum	Mar. 31, 2014 Common stock, Class A	Mar. 31, 2013 Common stock, Class A	Nov. 30, 2012 First Repurchase Plan Common stock, Class A	May 06, 2014 Subsequent Event [Member] Second Repurchase Plan Common stock, Class A
Class of Stock [Line Items]
Classes of common shares	2
Minimum number of directors up for election to entitle shareholders to vote	3
Minumum percent of directors up for election to entitle shareholders to vote	33.33%
Stock repurchase program, authorized amount									$ 100,000,000	$ 100,000,000
Stock repurchased during period, value	$ 17,828,000	$ 10,648,000					$ 17,800,000	$ 10,600,000
Range of price of shares repurchased (USD per share)			$ 16.35	$ 10.83	$ 19.99	$ 11.77