Share-Based Compensation and Capital Stock Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 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		$ 5,700
Aggregate intrinsic value of stock options, outstanding	$ 33,400		33,400
Aggregate intrinsic value of stock options, exercisable	26,500		26,500
Intrinsic value of stock options exercised	100		8,600		1,300
Proceeds from exercise of stock options	$ 100		$ 5,696		$ 1,547
Stock options exercised (in shares)	3,829	0	232,792		58,749
Share-based Compensation Expense	$ 2,900	$ 1,800	$ 5,700		$ 4,800
Periodic dividend (in dollars per share)			$ 0.195
Cash dividends declared per share (in dollars per share)	$ 0.195	$ 0.185	$ 0.39		$ 0.37
Dividends declared	$ 11,200	$ 10,800	$ 22,500		$ 21,600
Common stock purchased under stock repurchase program (in shares)	0	0	0		0
Shares redeemed for tax withholding for share based compensation (in shares)	296	302	102,753		94,745
Payments related to tax withholding for share-based compensation	$ 19	$ 13	$ 6,200		$ 4,500
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		$ 1,400
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	$ 300	$ (800)	$ 600		$ (100)
Dividends declared			500		400
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	$ (200)	$ (1,200)	$ (200)		$ (1,000)
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 six months ended June 30, 2015.