Stock Based Compensation (Narrative) (Details) - USD ($)	1 Months Ended				12 Months Ended
	Jan. 31, 2016	Jul. 31, 2015	Jan. 31, 2015	Jul. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture rate					5.00%	5.00%	5.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)					$ 63.09
Number of shares granted					366,200
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)					$ 61.82
Number of shares granted					355,688
Long-Term Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's common stock authorized to employees (in shares)								5,300,000
Long-Term Equity Incentive Plan | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU vesting terms for employees and directors					33.00%
Vesting period (in years)					3 years
Compensation expense					$ 22,001,000	$ 23,856,000	$ 26,734,000
Compensation expenses income tax benefit					7,696,000	$ 8,337,000	$ 9,343,000
Weighted average grant date fair value (in dollars per share)						$ 65.14	$ 45.27
Unrecognized compensation cost					$ 12,931,000
Unrecognized compensation cost expected to be recognized over a weighted-average period (in years)					1 year 21 days
Fair value of shares vested and issued during the period					$ 35,771,000	$ 35,206,000	$ 24,812,000
Long-Term Equity Incentive Plan | Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payout level minimum					0.00%
Percentage of payout level maximum					150.00%
Percentage of payout level target					100.00%
Revenues benchmark for performance payout					$ 1,000,000
Compensation expense					15,523,000	24,380,000	22,257,000
Compensation expenses income tax benefit					5,428,000	$ 8,516,000	$ 7,774,000
Weighted average grant date fair value (in dollars per share)						$ 64.93	$ 44.22
Unrecognized compensation cost					$ 16,920,000
Unrecognized compensation cost expected to be recognized over a weighted-average period (in years)					280 days
Fair value of shares vested and issued during the period					$ 27,461,000	$ 31,609,000
Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's common stock authorized to employees (in shares)					10,000,000
Number of shares granted					0
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's common stock authorized to employees (in shares)					5,000,000
Compensation expense					$ 1,277,000	1,201,000	$ 1,098,000
Compensation expenses income tax benefit					$ 186,000	$ 147,000	$ 208,000
Percentage of stock price purchased					90.00%
Participants' maximum contribution per offering period					$ 7,500.0
Participants' maximum contribution per year					$ 15,000
Number of hours worked					20 hours
Permanent employee work eligibility (months worked per year)					5 months
Number of continuous months worked					6 months
Non temporary employee requirement (months employed)					12 months
Maximum number of days for leave of absence					90 days
Maximum number of shares can be purchased each offering period per employee					5,000
Common shares issued		65,320	65,302	65,867
Discounted price of shares issued (in dollars per share)		$ 60.30		$ 58.79	$ 59.65
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be issued as a percentage of initial target					0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be issued as a percentage of initial target					150.00%
Subsequent Event | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares issued	59,102
Discounted price of shares issued (in dollars per share)	$ 61.70