Equity, Voting Rights and Stock Award and Incentive Plan (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) VoteperShare Plan $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Stock Award and Incentive Plan [Abstract]
Number of incentive plans | Plan		2
RSAs, weighted average grant date fair value [Abstract]
Stock compensation expense recognized due to acceleration of lapsing of restrictions on RSAs	$ 3,500,000
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Compensation cost related to non-vested restricted stock awards and options not yet recognized		$ 7,300,000
Projected compensation cost not yet recognized [Abstract]
2017		2,541,000
2018		1,718,000
2019		1,379,000
2020		748,000
2021		505,000
2022		306,000
2023		130,000
2024		21,000
Stock based compensation expense		3,959,000	$ 9,868,000	$ 5,278,000
Tax benefit from compensation expense		$ 1,500,000	3,700,000	2,000,000
Proceeds from exercise of stock options			1,167,000	1,637,000
Tax benefit from exercise of stock options			$ 102,000	$ 349,000
Class A [Member]
Voting Rights [Abstract]
Number of votes per share | VoteperShare		1
Class A [Member] | Maximum [Member]
Stock Award and Incentive Plan [Abstract]
Number of shares reserved for issuance under each plan (in shares) | shares		4,000,000
Class B [Member]
Voting Rights [Abstract]
Number of votes per share | VoteperShare		10
Stock Options [Member]
Options, shares [Roll Forward]
Outstanding, beginning of period (in shares) | shares		0	26,000
Granted (in shares) | shares		0	0
Forfeited (in shares) | shares		0	0
Exercised (in shares) | shares		0	(26,000)
Outstanding, end of period (in shares) | shares	0	0	0	26,000
Shares available for future issuance, end of period (in shares) | shares		51,530
Options, weighted average exercise price [Roll Forward]
Outstanding, beginning of period (in dollars per share) | $ / shares		$ 0	$ 44.89
Granted (in dollars per share) | $ / shares		0	0
Forfeited (in dollars per share) | $ / shares		0	0
Exercised / Vested (in dollars per share) | $ / shares		0	39.55
Outstanding, end of period (in dollars per share) | $ / shares	$ 0	$ 0	$ 0	$ 44.89
RSAs, weighted average grant date fair value [Abstract]
Options exercisable (in shares) | shares				23,500
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares				$ 44.80
Stock Options [Member] | Maximum [Member]
Stock Award and Incentive Plan [Abstract]
Term of nonqualified stock options		10 years
Stock Options [Member] | Vesting in Three Years from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		75.00%
Award vesting period		3 years
Restricted Stock Awards [Member]
RSAs, shares [Roll Forward]
Outstanding, beginning of period (in shares) | shares		553,100	710,750
Granted (in shares) | shares		0	0	158,600
Forfeited (in shares) | shares		(9,300)	(27,000)
Vested (in shares) | shares		(119,460)	(130,650)
Outstanding, end of period (in shares) | shares	553,100	424,340	553,100	710,750
RSAs, weighted average grant date fair value [Abstract]
Outstanding, beginning of period (in dollars per share) | $ / shares		$ 64.02	$ 67.45
Granted (in dollars per share) | $ / shares		0	0	$ 80.23
Forfeited (in dollars per share) | $ / shares		64.85	69.50
Vested (in dollars per share) | $ / shares		57.86	81.55
Outstanding, end of period (in dollars per share) | $ / shares	$ 64.02	$ 65.74	$ 64.02	$ 67.45
Stock compensation expense recognized due to acceleration of lapsing of restrictions on RSAs			$ 3,500,000
Restricted Stock Awards [Member] | Vesting in Three Years from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		30.00%
Award vesting period		3 years
Restricted Stock Awards [Member] | Vesting in Five Years from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		70.00%
Award vesting period		5 years
Restricted Stock Awards [Member] | Vesting in Year Four from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Restricted Stock Awards [Member] | Vesting in Year Five from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Restricted Stock Awards [Member] | Vesting in Year Six from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Restricted Stock Awards [Member] | Vesting in Year Seven from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Restricted Stock Awards [Member] | Vesting in Year Eight from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Restricted Stock Awards [Member] | Vesting in Year Nine from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Restricted Stock Awards [Member] | Vesting in Year Ten from Date of Grant [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		10.00%
Mr. Gabelli [Member] | Restricted Stock Awards [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		25.00%
Deferred compensation agreement, value of shares issued		$ 18,991,316
Mr. Gabelli [Member] | Restricted Stock Awards [Member] | Vesting on January 1, 2020 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		100.00%
Mr. Gabelli [Member] | Restricted Stock Awards [Member] | Class A [Member]
RSAs, weighted average grant date fair value [Abstract]
Deferred compensation agreement, shares issued (in shares) | shares		2,314,695
Deferred compensation agreement, share price (in dollars per share) | $ / shares		$ 32.8187
Deferred compensation agreement, value of shares issued		$ 75,965,266
Closing price (in dollars per share) | $ / shares		$ 30.89
Reduction of RSU expense		$ (1,116,082)
Mr. Gabelli [Member] | Award Granted on December 21, 2015 [Member] | Vesting on January 1, 2020 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		100.00%
Mr. Gabelli [Member] | Award Granted on December 21, 2015 [Member] | Vesting in 2016 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		25.00%
Mr. Gabelli [Member] | Award Granted on December 21, 2015 [Member] | Vesting in 2017 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		25.00%
Mr. Gabelli [Member] | Award Granted on December 21, 2015 [Member] | Vesting in 2018 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		25.00%
Mr. Gabelli [Member] | Award Granted on December 23, 2016 [Member] | Restricted Stock Awards [Member] | Vesting on July 1, 2018 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		100.00%
Mr. Gabelli [Member] | Award Granted on December 23, 2016 [Member] | Restricted Stock Awards [Member] | Vesting in 2017 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		67.00%
Mr. Gabelli [Member] | Award Granted on December 23, 2016 [Member] | Restricted Stock Awards [Member] | Vesting in 2018 [Member]
RSAs, weighted average grant date fair value [Abstract]
Award vesting percentage		33.00%