Consolidated Statements Of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2017		286,752
Shareholders' Equity beginning of period at Dec. 31, 2017	$ 4,154,026	$ 2,868	$ 3,171,542	$ (445)	$ 980,061
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	22,411		0		22,411
Stock option exercises (shares)		284
Stock option exercises	2,723	$ 3	2,720
Stock issuances, net of cancellations (shares)		783
Stock issuances, net of cancellations	3,485	$ 8	3,477
Dividends declared	(26,051)				(26,051)
Share repurchases (shares)		(1,941)
Share repurchases	(59,491)	$ (20)			(59,471)
Share-based compensation	6,782		6,782
Net income	170,751				170,751
Other comprehensive income	21			21
Shareholders' Equity, shares end of period (shares) at Mar. 31, 2018		285,878
Shareholders' Equity end of period at Mar. 31, 2018	4,274,657	$ 2,859	3,184,521	(424)	1,087,701
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2018		277,110
Shareholders' Equity beginning of period at Dec. 31, 2018	4,817,782	$ 2,771	3,201,427	(345)	1,613,929
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises (shares)		118
Stock option exercises	1,445	$ 1	1,444
Stock issuances, net of cancellations (shares)		1,337
Stock issuances, net of cancellations	5,804	$ 12	5,792
Dividends declared	(30,831)				(30,831)
Share repurchases (shares)		(1,309)
Share repurchases	(35,353)	$ (13)			(35,340)
Share-based compensation	7,810		7,810
Net income	166,757				166,757
Other comprehensive income	25			25
Shareholders' Equity, shares end of period (shares) at Mar. 31, 2019		277,256
Shareholders' Equity end of period at Mar. 31, 2019	$ 4,933,439	$ 2,771	$ 3,216,473	$ (320)	$ 1,714,515