Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock, Common [Member]	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
September 30, 2019 at Dec. 31, 2017	$ 4,206,653	$ 3,091		$ 1,141,451	$ 3,124,103	$ (70,476)	$ 8,484
September 30, 2019 at Dec. 31, 2017		309,127
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	445,109				444,069		1,040
Other comprehensive loss	(69,660)					(69,660)
Stock issued in acquisitions		8,056
Stock issued in acquisitions	251,334	$ 81		251,253
Vesting of restricted stock units, net of shares withheld for employee tax		600
Vesting of restricted stock units, net of shares withheld for employee tax	(3,711)	$ 6		(3,717)	0	0	0
Stock-based compensation expense	17,544			17,544
Exercise of stock options		441
Exercise of stock options	3,772	$ 4		3,768
Shares withheld for net share settlement of stock option awards		(27)
Shares withheld for net share settlement of stock option awards	1,057			1,057
Adoption of ASU 2018-02 (see Note 9)	5,345				(5,345)	5,345
Capital contributions from, net of dividends declared to, noncontrolling interest shareholder	3,182						3,182
Acquired noncontrolling interest	44,250						44,250
September 30, 2019 at Sep. 30, 2018	4,897,416	$ 3,182		1,409,242	3,562,827	(134,791)	56,956
September 30, 2019 at Sep. 30, 2018		318,197
Increase (Decrease) in Stockholders' Equity [Roll Forward]
September 30, 2019			(2,272)
September 30, 2019 at Dec. 31, 2017	4,206,653	$ 3,091		1,141,451	3,124,103	(70,476)	8,484
September 30, 2019 at Dec. 31, 2017		309,127
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued in acquisitions	251,334
Acquired noncontrolling interest	44,110
September 30, 2019 at Dec. 31, 2018			(2,272)
September 30, 2019 at Dec. 31, 2018	4,838,752	$ 3,184	$ (60,000)	1,415,188	3,598,876	(174,950)	56,454
September 30, 2019 at Dec. 31, 2018		318,418
September 30, 2019 at Jun. 30, 2018	4,776,975	$ 3,178		1,403,630	3,428,725	(116,061)	57,503
September 30, 2019 at Jun. 30, 2018		317,821
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	134,480				134,102		(378)
Other comprehensive loss	(18,730)					(18,730)
Vesting of restricted stock units, net of shares withheld for employee tax		256
Vesting of restricted stock units, net of shares withheld for employee tax	(934)	$ 3		(937)
Stock-based compensation expense	5,700			5,700
Exercise of stock options		120
Exercise of stock options	850	$ 1		849
Capital contributions from, net of dividends declared to, noncontrolling interest shareholder	(925)						(925)
September 30, 2019 at Sep. 30, 2018	4,897,416	$ 3,182		1,409,242	3,562,827	(134,791)	56,956
September 30, 2019 at Sep. 30, 2018		318,197
Increase (Decrease) in Stockholders' Equity [Roll Forward]
September 30, 2019			(2,272)
September 30, 2019			(13,196)
September 30, 2019 at Dec. 31, 2018	4,838,752	$ 3,184	$ (60,000)	1,415,188	3,598,876	(174,950)	56,454
September 30, 2019 at Dec. 31, 2018		318,418
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	403,761				400,872		(2,889)
Other comprehensive loss	$ (85,796)					(85,796)
Purchase of treasury stock	(10,924)
Purchase of treasury stock	$ (291,813)
Stock issued in acquisitions	0
Vesting of restricted stock units, net of shares withheld for employee tax		684
Vesting of restricted stock units, net of shares withheld for employee tax	(1,801)	$ 7		(1,808)
Stock-based compensation expense	20,837			20,837
Exercise of stock options		606
Exercise of stock options	5,468	$ 6		5,462
Shares withheld for net share settlement of stock option awards		(110)
Shares withheld for net share settlement of stock option awards	(3,534)	$ (1)		(3,533)
Capital contributions from, net of dividends declared to, noncontrolling interest shareholder	(4,659)						(4,659)
Acquired noncontrolling interest	10,365						10,365
Purchase of noncontrolling interest (2)	(18,880)			(8,764)			(10,116)
September 30, 2019 at Sep. 30, 2019			(13,196)
September 30, 2019 at Sep. 30, 2019	4,872,700	$ 3,196	$ (351,813)	1,427,382	3,999,748	(260,746)	54,933
September 30, 2019 at Sep. 30, 2019		319,598
Increase (Decrease) in Stockholders' Equity [Roll Forward]
September 30, 2019			(9,315)
September 30, 2019			(13,196)
September 30, 2019 at Jun. 30, 2019	4,909,748	$ 3,190	$ (250,762)	1,429,129	3,847,485	(188,553)	69,259
September 30, 2019 at Jun. 30, 2019		319,010
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	152,593				152,263		(330)
Other comprehensive loss	$ (72,193)					(72,193)
Purchase of treasury stock	(3,881)
Purchase of treasury stock	$ (101,051)
Vesting of restricted stock units, net of shares withheld for employee tax		313
Vesting of restricted stock units, net of shares withheld for employee tax	(647)	$ 3		(650)
Stock-based compensation expense	7,178			7,178
Exercise of stock options		370
Exercise of stock options	$ 3,598	$ 4		3,594
Shares withheld for net share settlement of stock option awards	(95)
Shares withheld for net share settlement of stock option awards	$ 3,106	(1)		(3,105)
Capital contributions from, net of dividends declared to, noncontrolling interest shareholder	(4,644)						(4,644)
Acquired noncontrolling interest	104						104
Purchase of noncontrolling interest (2)	(18,880)			(8,764)			(10,116)
September 30, 2019 at Sep. 30, 2019			(13,196)
September 30, 2019 at Sep. 30, 2019	$ 4,872,700	$ 3,196	$ (351,813)	$ 1,427,382	$ 3,999,748	$ (260,746)	$ 54,933
September 30, 2019 at Sep. 30, 2019		319,598
Increase (Decrease) in Stockholders' Equity [Roll Forward]
September 30, 2019			(13,196)