Stockholders' Equity (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended
	Aug. 07, 2015	Jun. 30, 2015	Jun. 30, 2015	Jan. 30, 2015
2006 Equity Incentive Plan (2006 Plan)
Stockholders' equity
Common stock reserved for issuance (in shares)		6,000,000	6,000,000
Maximum number of shares that may be issued through the exercise of incentive stock options		4,500,000	4,500,000
Compensation cost not yet recognized		$ 13,900,000	$ 13,900,000
2006 Equity Incentive Plan (2006 Plan) | Nonvested stock units issued (NSUs)
Stockholders' equity
Number of shares granted		183,000
NSUs granted that will vest at the end of each of the three years after the performance goals are achieved (as a percent)		33.33%
2006 Equity Incentive Plan (2006 Plan) | Time-based equity award
Stockholders' equity
Number of shares granted		5,000
Weighted average grant date fair value		$ 74.23
Award vesting period of the grants		3 years
2015 Stock Repurchase Program
Stockholders' equity
Maximum stock repurchase amount approved by Board of Directors				$ 200,000,000
Treasury stock, shares, acquired		625,000
Treasury stock, value, acquired		$ 45,400,000
Treasury stock acquired, average cost per share		$ 72.69	$ 73.21
Treasury stock, number of shares held		1,002,000	1,002,000
Treasury stock, value		$ 73,300,000	$ 73,300,000
Remaining stock repurchase amount approved by Board of Directors		$ 126,700,000	$ 126,700,000
Subsequent Event | 2015 Stock Repurchase Program
Stockholders' equity
Treasury stock, shares, acquired	57,000
Treasury stock, value, acquired	$ 4,000,000
Treasury stock acquired, average cost per share	$ 69.61
Remaining stock repurchase amount approved by Board of Directors	$ 122,700,000