Accounting Changes (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		9 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
New Accounting Pronouncement, Early Adoption [Line Items]
Net cash provided by operating activities						$ 160,111	$ 160,596
Net cash used by financing activities						(19,033)	(46,611)
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Excess tax benefits recognized in provision for income taxes	$ 1,530					1,530
State tax loss carryforwards recognized	195					195
Net cash provided by operating activities		$ 413	$ 1,402	$ 524	$ 2,320		7,519
Net cash used by financing activities		$ 413	$ 1,402	$ 524	$ 2,320		$ 7,519
Deferred tax assets, current	26,072					26,072
Deferred tax liabilities current	$ 1,173					$ 1,173