CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Comprehensive income:
Net income	$ 466,802	$ 455,188	$ 453,383
Derivative instruments:
Net fair value (decrease) increase, net of tax of $(20), $(43) and $5, respectively	(30)	(72)	9
Reclassification of losses (gains) to net income, net of tax of $39, $(287) and $(294), respectively	72	(468)	(476)
Other comprehensive income (loss)	42	(540)	(467)
Comprehensive income	$ 466,844	$ 454,648	$ 452,916