Capital Stock - Narrative (Details)		12 Months Ended
	Dec. 23, 2015 vote / shares vote $ / shares	Dec. 22, 2015 vote / shares $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Class of Stock [Line Items]
Common stock, shares, outstanding (shares)			54,882,154	55,532,307
Common stock, par value (USD per share) | $ / shares			$ 0.01	$ 0.01
Voting rights, percentage		36.00%
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares, outstanding (shares)			0	0	0	7,167,000
Reclassification of stock, proposed premium per share (USD per share) | $ / shares	$ 28.00
Common stock, voting rights (votes per share) | vote / shares		20
Class B Common Stock
Class of Stock [Line Items]
Common stock, shares, outstanding (shares)			0	0	0	51,329,000
Common stock, par value (USD per share) | $ / shares	$ 0.01
Common stock, voting rights (votes per share) | vote / shares		1
Common Stock
Class of Stock [Line Items]
Common stock, shares, outstanding (shares)			54,882,000	55,532,000	57,837,000	0
Reclassification of stock, voting rights of proposed share class (vote) | vote	1
Common stock, voting rights (votes per share) | vote / shares	1
Louie E. Roche Trust and Harvey Hubbell Trust | Class A Common Stock
Class of Stock [Line Items]
Common stock, shares, outstanding (shares)		3,488,460
Common stock, par value (USD per share) | $ / shares		$ 0.01
Ownership percentage, by shareholder		49.00%