Capital Stock - Narrative (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) director common_share $ / shares	May. 31, 2014 USD ($)
Class of Stock [Line Items]
Classes of common shares | common_share	2
Minimum number of directors up for election to entitle shareholders to vote | director	3
Stock repurchased during period, value	$ 10,131,000
Common stock, Class A
Class of Stock [Line Items]
Stock repurchase program, authorized amount		$ 100,000,000
Stock repurchased during period, value	10,100,000
Stock repurchase program, remaining authorized amount	$ 73,600,000
Common stock, Class A | Minimum
Class of Stock [Line Items]
Stock repurchased during period (in dollars per share) | $ / shares	$ 16.01
Common stock, Class A | Maximum
Class of Stock [Line Items]
Stock repurchased during period (in dollars per share) | $ / shares	$ 19.51