Stock-based Compensation - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Aggregate number of shares of common stock issued or transferred under the incentive stock awards plan (in shares)	2,380,572
Stock based compensation expense	$ 27,400,000	$ 21,500,000	$ 14,200,000
Tax benefit from exercise of stock options	10,400,000	8,200,000	5,400,000
Excess tax benefit from share-based compensation, operating activities	$ 1,100,000		$ 300,000
Excess tax (deductions) benefits included in cash provided by operating activities		$ (700,000)
Stock options granted (in shares)	518,000	634,000	338,000
Aggregate Intrinsic value of options exercised	$ 2,600,000	$ 400,000	$ 800,000
Fair value of options vested	$ 1,700,000	1,400,000	1,100,000
Employee Service Share-based Compensation, Cash Flow Effect, Cash Used to Settle Awards		$ 0	$ 0
2001 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unexercised options lapse period (in years)	10 years
2015 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unexercised options lapse period (in years)	10 years
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unrecognized compensation expense related to non-vested award	$ 24,400,000
Unrecognized compensation expense related to non-vested award, recognition period (in years)	1 year 6 months 26 days
Stock options | Minimum | 2001 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	1 year
Stock options | Minimum | 2015 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	1 year
Stock options | Maximum | 2001 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	5 years
Stock options | Maximum | 2015 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	3 years
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock granted (in shares)	375,000	379,000	261,000
Weighted average grant date fair value (in dollars per share)	$ 29.27	$ 22.81	$ 31.78
Total fair value of shares vesting	$ 9,900,000	$ 3,800,000	$ 1,800,000
Restricted Stock | Executive Officer Performance Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	3 years
Restricted Stock | Minimum | 2001 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	1 year
Restricted Stock | Minimum | 2015 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	1 year
Restricted Stock | Minimum | AMP Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	4 years
Restricted Stock | Maximum | 2001 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	5 years
Restricted Stock | Maximum | 2015 Incentive Award Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	3 years
Restricted Stock | Maximum | AMP Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	5 years
Performance Share Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock granted (in shares)	479,000
Weighted average grant date fair value (in dollars per share)	$ 27.00
Total fair value of shares vesting	$ 7,900,000	$ 3,400,000	$ 0
Performance Share Units | Minimum
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Performance percentage	0.00%
Performance Share Units | Maximum
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Performance percentage	200.00%
Performance criteria is met | Performance Share Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award vesting rights (percentage)	33.33%
One-year service period | Performance Share Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Vesting period (in years)	1 year
Award vesting rights (percentage)	33.33%
Award requisite service period (in years)	1 year
Two-year service period | Performance Share Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award vesting rights (percentage)	33.33%
Award requisite service period (in years)	2 years