CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Class A Common Stock	Paid-in Capital	Retained Earnings	Total
Balance at Dec. 31, 2013	$ 1,009	$ 2,209,566	$ 312,859	$ 2,523,434
Balance (in shares) at Dec. 31, 2013	101,822,676
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon exercise of options and vesting of restricted stock units	$ 1	943		944
Issuance of common stock upon exercise of options and vesting of restricted stock units (in shares)	1,028,654
Stock-based compensation expense		16,048		16,048
Cash dividends (declared $0.13, $0.17,$0.225 per share for December 31, 2014, 2015 and 2016, respectively )			(13,284)	(13,284)
Tax benefits from stock based compensation arrangements		7,011		7,011
Tax withholdings on stock based compensation		(18,089)		(18,089)
Tax withholdings on stock based compensation (in shares)	(459,122)
Net income			255,998	255,998
Balance at Dec. 31, 2014	$ 1,010	2,215,479	555,573	2,772,062
Balance (in shares) at Dec. 31, 2014	102,392,208
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon exercise of options and vesting of restricted stock units		177		177
Issuance of common stock upon exercise of options and vesting of restricted stock units (in shares)	321,395
Stock-based compensation expense		17,022		17,022
Cash dividends (declared $0.13, $0.17,$0.225 per share for December 31, 2014, 2015 and 2016, respectively )			(17,438)	(17,438)
Tax withholdings on stock based compensation		(5,302)		(5,302)
Tax withholdings on stock based compensation (in shares)	(130,934)
Net income			253,391	253,391
Balance at Dec. 31, 2015	$ 1,010	2,227,376	791,526	3,019,912
Balance (in shares) at Dec. 31, 2015	102,582,669
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon exercise of options and vesting of restricted stock units		96		96
Issuance of common stock upon exercise of options and vesting of restricted stock units (in shares)	452,759
Stock-based compensation expense		16,941		16,941
Cash dividends (declared $0.13, $0.17,$0.225 per share for December 31, 2014, 2015 and 2016, respectively )			(23,140)	(23,140)
Tax withholdings on stock based compensation		(6,547)		(6,547)
Tax withholdings on stock based compensation (in shares)	(190,951)
Net income			374,925	374,925
Balance at Dec. 31, 2016	$ 1,010	$ 2,237,866	$ 1,143,311	$ 3,382,187
Balance (in shares) at Dec. 31, 2016	102,844,477