Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Accumulated other comprehensive earnings [Member]	Noncontrolling interest [Member]
Beginning balance (in shares) at Dec. 31, 2014		0	34,756,384	11,486,932
Beginning balance at Dec. 31, 2014	$ 1,725,678	$ 0	$ 348	$ 115	$ 17,290	$ 1,702,560	$ 5,135	$ 230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of noncontrolling interests	7,443							7,443
Net income	268,264					267,979		285
Other comprehensive income (loss)	(2,851)						(2,851)
Distribution to noncontrolling interests	(232)							(232)
Cash dividends on Class A and Class B common stock	(19,025)					(19,025)
Issuance of common stock, net of forfeitures (in shares)			159,303
Issuance of common stock, net of forfeitures	3,862		$ 2		3,860
Compensation expense for stock based awards	5,188				5,188
Repurchase of common stock (in shares)			(2,449,159)
Repurchase of common stock	(96,169)		$ (25)		(26,338)	(69,806)
Conversion of of common stock (in shares)			10,000	(10,000)
Ending balance at Dec. 31, 2015	1,892,158	$ 0	$ 325	$ 115	0	1,881,708	2,284	7,726
Ending balance (in shares) at Dec. 31, 2015		0	32,476,528	11,476,932
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of noncontrolling interests	1,366							1,366
Net income	257,501					256,751		750
Other comprehensive income (loss)	2,446						2,446
Distribution to noncontrolling interests	(572)							(572)
Cash dividends on Class A and Class B common stock	(21,188)					(21,188)
Issuance of common stock, net of forfeitures (in shares)			189,952
Issuance of common stock, net of forfeitures	4,219		$ 1		4,218
Compensation expense for stock based awards	4,086				4,086
Repurchase of common stock (in shares)			(2,038,368)
Repurchase of common stock	(69,091)		$ (20)		(7,884)	(61,187)
Ending balance at Dec. 31, 2016	2,070,925	$ 0	$ 306	$ 115	420	2,056,084	4,730	9,270
Ending balance (in shares) at Dec. 31, 2016		0	30,628,112	11,476,932
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of noncontrolling interests	19,578							19,578
Net income	161,821					173,166		(11,345)
Other comprehensive income (loss)	(113)						(113)
Distribution to noncontrolling interests	(1,645)							(1,645)
Cash dividends on Class A and Class B common stock	(24,097)					(24,097)
Issuance of common stock, net of forfeitures (in shares)			178,114
Issuance of common stock, net of forfeitures	3,621		$ 2		3,619
Compensation expense for stock based awards	4,193				4,193
Repurchase of common stock (in shares)			(1,473,054)
Repurchase of common stock	(68,896)		$ (15)		(7,711)	(61,170)
Conversion of of common stock (in shares)			8,345	(8,345)
Ending balance at Dec. 31, 2017	$ 2,165,387	$ 0	$ 293	$ 115	$ 521	$ 2,143,983	$ 4,617	$ 15,858
Ending balance (in shares) at Dec. 31, 2017		0	29,341,517	11,468,587