Stock-Based Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2018

Summary of Stock Options Issued Pursuant to Stock Incentive Plans

A summary of stock options issued pursuant to the Company’s stock incentive plans is as follows:

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value  of In-the-Money Options
Outstanding as of December 31, 2017		6,162,717		$	16.83
Granted		170,455			23.36
Exercised		(656,898	)		13.88
Forfeited		(3,255	)		17.89
Outstanding as of March 31, 2018		5,673,019		$	17.37		6.74	$	36,025,874
Exercisable as of March 31, 2018		4,081,780		$	16.58		6.11	$	29,135,028

Black-Scholes Option-Pricing Model [Member]

Estimated Fair Value of Options Granted Pricing Model with Weighted-Average Assumptions

The fair value of options that do not vest based on the achievement of certain market conditions granted during the three months ended March 31, 2018 and 2017 were estimated on the date of grant using the Black-Scholes option-pricing model, a pricing model acceptable under U.S. GAAP, with the following weighted-average assumptions:

	Three Months Ended March 31, 2018			Three Months Ended March 31, 2017
Expected life (years)		5.6			5.6
Interest rate		2.7	%		1.9	%
Volatility		26.4	%		29.4	%
Dividend yield		—			—

LTIP Performance Shares [Member]

Summary of Nonvested Performance Share Awards and Changes During Period

A summary of nonvested long-term incentive program performance share awards (“LTIP performance shares”) outstanding as of March 31, 2018 and changes during the period are as follows:

Nonvested LTIP Performance Shares	Number of Shares at Expected Attainment			Weighted- Average Grant Date Fair Value
Nonvested as of December 31, 2017		1,125,035		$	18.94
Forfeited		(8,008	)		19.57
Nonvested as of March 31, 2018		1,117,027		$	18.94

Total Shareholder Return [Member] | Monte Carlo Simulation [Member]

Estimated Fair Value of Options Granted Pricing Model with Weighted-Average Assumptions

The grant date fair value of the TSRs was estimated using the following weighted-average assumptions:

	Three Months Ended March 31, 2018			Three Months Ended March 31, 2017
Expected life (years)		2.9			2.9
Interest rate		2.4	%		1.5	%
Volatility		28.0	%		26.5	%
Dividend Yield		—			—

TSR Plan [Member]

Summary of Nonvested Performance Share Awards and Changes During Period

A summary of nonvested TSRs outstanding as of March 31, 2018 and changes during the period are as follows:

Nonvested Total Shareholder Return Awards	Number of Shares at Expected Attainment			Weighted- Average Grant Date Fair Value
Nonvested as of December 31, 2017		143,649		$	24.37
Granted		541,214			31.31
Forfeited		(1,837	)		31.31
Nonvested as of March 31, 2018		683,026		$	29.85

Restricted Share Awards (RSAs) [Member]

Summary of Nonvested Restricted Share and Changes During Period

A summary of nonvested restricted share awards (“RSAs”) as of March 31, 2018 and changes during the period are as follows:

Nonvested Restricted Share Awards	Number of Restricted Share Awards			Weighted-Average Grant Date Fair Value
Nonvested as of December 31, 2017		503,237		$	20.63
Vested		(123,427	)		20.12
Forfeited		(10,727	)		20.12
Nonvested as of March 31, 2018		369,083		$	20.81

Performance-Based Restricted Share Awards [Member]

Summary of Nonvested Performance Share Awards and Changes During Period

A summary of nonvested Performance-Based Restricted Share Awards (“PBRSAs”) as of March 31, 2018 and changes during the period are as follows:

Nonvested Performance-Based Restricted Share Awards	Number of Performance-Based Restricted Share Awards		Weighted-Average Grant Date Fair Value
Nonvested as of December 31, 2017		173,636	$	24.41
Nonvested as of March 31, 2018		173,636	$	24.41

Restricted Share Units [Member]

Summary of Nonvested Restricted Share and Changes During Period

A summary of nonvested RSUs as of March 31, 2018 and changes during the period are as follows:

Nonvested Restricted Share Units	Number of Restricted Share Units			Weighted- Average Grant Date Fair Value
Nonvested as of December 31, 2017		—		$	—
Granted		581,945			23.36
Forfeited		(2,461	)		23.36
Nonvested as of March 31, 2018		579,484		$	23.36