Common Stock Options, Restricted Stock and Changes In Capitalization (Details) - USD ($)				12 Months Ended			44 Months Ended
	Feb. 17, 2017	Dec. 21, 2016	Mar. 15, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2016	May 31, 2018	Jan. 31, 2018	Apr. 19, 2013	Apr. 20, 2006	Apr. 19, 2006
Class of Stock [Line Items]
Granted for purchase of previous plan's common stock (shares)				0	0	0
Proceeds from issuance of common stock, net of offering costs and exercise of stock options		$ 698,800,000	$ 411,700,000		$ (5,364,000)	$ 1,110,555,000
Stock repurchase program, authorized amount								$ 200,000,000	$ 100,000,000
Stock repurchase program, additional authorized amount								$ 100,000,000
Stock repurchased and retired during period (shares)				20,700,000
Stock repurchased and retired during period, net of tax				$ 200,000,000
Shares repurchased for tax withholding requirement (in shares)				29,000
Tax withholding requirement				$ 300,000
Vitruvian
Class of Stock [Line Items]
Total initial price	$ 1,850,000,000
Payments to acquire businesses	$ 1,354,093,000
Equity interest issued or issuable, number of shares (in shares)	23,900,000
Vitruvian | Indemnity Escrow
Class of Stock [Line Items]
Equity interest issued or issuable, number of shares (in shares)	5,200,000
Common Stock
Class of Stock [Line Items]
Issuance of common stock in public offering (shares)		33,350,000	16,905,000			50,255,000
Stock repurchased and retired during period (shares)				20,746,536
2005 Stock Incentive Plan | Common Stock
Class of Stock [Line Items]
Available for grant (shares)											3,000,000	1,904,606
Granted for purchase of previous plan's common stock (shares)				997,269
1999 Stock Option Plan | Common Stock
Class of Stock [Line Items]
Granted to employees under previous plan (shares)											627,337
2013 Restated Stock Incentive Plan | Common Stock
Class of Stock [Line Items]
Available for grant (shares)				3,518,964						7,500,000	3,000,000
Granted for purchase of previous plan's common stock (shares)							627,337
Over-allotment option | Common Stock
Class of Stock [Line Items]
Issuance of common stock in public offering (shares)		4,350,000	2,205,000
Restricted stock | 2005 Stock Incentive Plan
Class of Stock [Line Items]
Granted for purchase of previous plan's common stock (shares)				1,143,217