CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Class A Common Stock	Class A Common Stock Common Stock	Class B Common Stock	Class B Common Stock Common Stock
BALANCE (shares) at Dec. 31, 2017							76,071,145		25,670,684
BALANCE at Dec. 31, 2017	$ 1,534,366	$ 1,320,298	$ 248,845	$ (1,423)	$ (34,372)		$ 761		$ 257
Cumulative effect of adoption of new accounting standard at Dec. 31, 2017	2,100		2,100
Increase (Decrease) in Stockholders' Equity
Dividends declared and paid on Class A and Class B Common Stock	(36,794)		(36,794)
Class A Common Stock issued pursuant to employee benefit plans (shares)							505,835
Class A Common Stock issued pursuant to employee benefit plans	15,958	15,953					$ 5
Distributions to noncontrolling interests, net	(3,516)				(3,516)
Net income	73,304		71,165		2,139
BALANCE (shares) at Jun. 30, 2018							76,576,980		25,670,684
BALANCE at Jun. 30, 2018	1,585,418	1,336,251	285,316	(1,423)	(35,749)		$ 766		$ 257
BALANCE (shares) at Mar. 31, 2018							76,509,574		25,670,684
BALANCE at Mar. 31, 2018	1,571,543	1,332,432	275,676	(1,423)	(36,164)		$ 765		$ 257
Increase (Decrease) in Stockholders' Equity
Dividends declared and paid on Class A and Class B Common Stock	(18,401)		(18,401)
Class A Common Stock issued pursuant to employee benefit plans (shares)							67,406
Class A Common Stock issued pursuant to employee benefit plans	3,820	3,819					$ 1
Distributions to noncontrolling interests, net	(853)				(853)
Net income	29,309		28,041		1,268
BALANCE (shares) at Jun. 30, 2018							76,576,980		25,670,684
BALANCE at Jun. 30, 2018	1,585,418	1,336,251	285,316	(1,423)	(35,749)		$ 766		$ 257
BALANCE (shares) at Dec. 31, 2018						68,897,723	68,897,723	25,670,684	25,670,684
BALANCE at Dec. 31, 2018	1,600,320	1,121,054	517,620	(784)	(38,516)		$ 689		$ 257
Increase (Decrease) in Stockholders' Equity
Dividends declared and paid on Class A and Class B Common Stock	(36,765)		(36,765)
Class B Common Stock converted into Class A Common Stock (in shares)							643,002		(643,002)
Class B Common Stock converted into Class A Common Stock	0						$ 7		$ (7)
Repurchases of Class A Common Stock (in shares)							(3,993,194)
Repurchases of Class A Common Stock	(125,034)	(124,994)					$ (40)
Class A Common Stock issued pursuant to employee benefit plans (shares)							1,484,557
Class A Common Stock issued pursuant to employee benefit plans	28,109	28,095					$ 14
Distributions to noncontrolling interests, net	(3,785)				(3,785)
Net income	66,154		63,969		2,185
BALANCE (shares) at Jun. 30, 2019						67,032,088	67,032,088	25,027,682	25,027,682
BALANCE at Jun. 30, 2019	1,528,999	1,024,155	544,824	(784)	(40,116)		$ 670		$ 250
BALANCE (shares) at Mar. 31, 2019							66,241,852		25,527,682
BALANCE at Mar. 31, 2019	1,519,153	1,038,332	520,936	(784)	(40,248)		$ 662		$ 255
Increase (Decrease) in Stockholders' Equity
Dividends declared and paid on Class A and Class B Common Stock	(18,409)		(18,409)
Class B Common Stock converted into Class A Common Stock (in shares)							500,000		(500,000)
Class B Common Stock converted into Class A Common Stock	0						$ 5		$ (5)
Repurchases of Class A Common Stock (in shares)							(500,000)
Repurchases of Class A Common Stock	(20,049)	(20,044)					$ (5)
Class A Common Stock issued pursuant to employee benefit plans (shares)							790,236
Class A Common Stock issued pursuant to employee benefit plans	5,875	5,867					$ 8
Distributions to noncontrolling interests, net	(954)				(954)
Net income	43,383		42,297		1,086
BALANCE (shares) at Jun. 30, 2019						67,032,088	67,032,088	25,027,682	25,027,682
BALANCE at Jun. 30, 2019	$ 1,528,999	$ 1,024,155	$ 544,824	$ (784)	$ (40,116)		$ 670		$ 250