Share-Based Compensation and Capital Stock Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Share-Based Compensation and Capital Stock [Line Items]
Stock options granted, shares	0	0	498,911		700,000
Stock options granted, fair value			$ 6,200,000		$ 5,700,000
Aggregate intrinsic value of stock options, outstanding	$ 21,600,000		21,600,000
Aggregate intrinsic value of stock options, exercisable	18,700,000		18,700,000
Intrinsic value of stock options exercised	900,000	$ 3,100,000	9,500,000		4,400,000
Proceeds from exercise of stock options	$ 700,000	$ 3,400,000	$ 6,381,000		$ 4,984,000
Stock options exercised (in shares)	30,808	131,808	263,600		190,557
Share-based Compensation Expense	$ 3,400,000	$ 3,100,000	$ 9,100,000		$ 7,900,000
Periodic dividend (in dollars per share)			$ 0.195
Cash dividends declared per share (in dollars per share)	$ 0.195	$ 0.185	$ 0.585		$ 0.555
Dividends declared	$ 11,000,000	$ 10,800,000	$ 33,500,000		$ 32,400,000
Common stock purchased under stock repurchase program (in shares)	1,000,000	400,000	1,000,000		400,000
Stock Repurchased During Period, Value	$ 50,000,000	$ 18,400,000	$ 50,000,000		$ 18,400,000
Shares redeemed for tax withholding for share based compensation (in shares)	3,512	15,834	106,265		110,579
Payments related to tax withholding for share-based compensation	$ 200,000	$ 800,000	$ 6,400,000		$ 5,300,000
Performance Vested Restricted Stock Units [Member]
Share-Based Compensation and Capital Stock [Line Items]
Grants vested (in shares)	0	0	42,326		28,886
Grants vested, total fair value			$ 1,500,000		$ 1,400,000
Grants vested, initial target (in shares)			38,476		18,635
Grants vested, performance percentage achieved			110.00%		155.00%
Increase in shares due to performance percentage achieved (in shares)			3,850	[1]	10,251
Share-based Compensation Expense	$ 1,000,000	$ 800,000	$ 1,600,000		$ 700,000
Dividends declared	0	$ 0	500,000		400,000
Performance Vested Restricted Stock Units [Member] | Revised estimate of projected achievement of performance conditions [Member]
Share-Based Compensation and Capital Stock [Line Items]
Share-based Compensation Expense	$ 400,000		$ 200,000		$ (900,000)
Performance Vested Restricted Stock Units [Member] | Minimum [Member]
Share-Based Compensation and Capital Stock [Line Items]
Vesting range (percentage)			0.00%
Award targets currently estimated to be achieved (percentage)			0.00%
Performance Vested Restricted Stock Units [Member] | Maximum [Member]
Share-Based Compensation and Capital Stock [Line Items]
Vesting range (percentage)			200.00%
Award targets currently estimated to be achieved (percentage)			180.00%

[1] PVRSU units outstanding have been increased by 3,850 units due to the Company exceeding the targeted performance conditions contained in PVRSUs granted in prior periods during the nine months ended September 30, 2015.