Business and Basis of Presentation - New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Basic earnings per share (in dollars per share)	$ 0.37	$ 0.63	$ 0.55	$ 0.37	$ 1.17	$ 1.54	$ 1.30
Diluted earnings per share (in dollars per share)	$ 0.36	$ 0.62	$ 0.54	$ 0.36	$ 1.15	$ 1.52	$ 1.29
Cash provided by operating activities		$ 148,452	$ 13,331		$ 161,783	$ 282,263	$ 266,307
Cash used in financing activities						(130,933)	(1,195)
Effective income tax rate reconciliation share based compensation excess tax benefit amount	$ 500					9,000
Provision for income taxes	14,264	25,565	15,320	$ 21,426	40,884	55,149	65,672
Net income	30,484	51,626	44,987	$ 30,366	96,614	127,097	$ 109,872
Accumulated earnings	$ 1,577,521	$ 1,547,037	$ 1,495,411		$ 1,547,037	$ 1,577,521		$ 1,450,684
Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Basic earnings per share (in dollars per share)		$ 0.58	$ 0.49		$ 1.07
Diluted earnings per share (in dollars per share)		$ 0.57	$ 0.48		$ 1.05
Cash provided by operating activities		$ 144,734	$ 8,580		$ 153,314
Provision for income taxes		29,280	20,140		49,420
Net income		47,911	40,167		88,078
Accumulated earnings		$ 1,538,762	$ 1,490,851		$ 1,538,762
Accounting Standards Update 2016-09 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Basic earnings per share (in dollars per share)	$ 0.01				$ 0.10	$ 0.11
Diluted earnings per share (in dollars per share)	$ 0.01				$ 0.10	$ 0.11
Accounting Standards Update 2016-09, Statutory Tax Withholding Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities					$ 8,500
Cash used in financing activities					$ (8,500)