Capital Stock (Details)		1 Months Ended	3 Months Ended	9 Months Ended
	Feb. 25, 2019 $ / shares shares	Nov. 30, 2016 USD ($)	Sep. 30, 2018 USD ($) shares	Sep. 30, 2019 USD ($) director common_share $ / shares	Sep. 30, 2018 USD ($) $ / shares
Class of Stock [Line Items]
Classes of common shares | common_share				2
Accelerated share repurchase program, agreement to repurchase		$ 25,000,000
Accelerated share repurchases, payment			$ 25,000,000		$ 25,000,000
Stock Repurchased and Retired During Period, Shares | shares	147,164		1,300,000
Accelerated Share Repurchase Program, Amount Of Shares Repurchased, Percent					80.00%
Treasury Stock Acquired, Average Cost Per Share | $ / shares	$ 16.70
Stock repurchased during period, value			$ 25,861,000	$ 584,000	$ 30,270,000
Minimum
Class of Stock [Line Items]
Minimum number of directors up for election to entitle shareholders to vote | director				0.3333
Maximum
Class of Stock [Line Items]
Minimum number of directors up for election to entitle shareholders to vote | director				3
Common stock, Class A
Class of Stock [Line Items]
Stock repurchase program, authorized amount		$ 100,000,000
Stock repurchased during period, value				$ 600,000	$ 5,300,000
Stock repurchase program, remaining authorized amount				$ 49,700,000
Common stock, Class A | Minimum
Class of Stock [Line Items]
Stock repurchased during period (in dollars per share) | $ / shares				$ 15.54	$ 13.29
Common stock, Class A | Maximum
Class of Stock [Line Items]
Stock repurchased during period (in dollars per share) | $ / shares				$ 18.72	$ 16.86