Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 219,299	$ 255,872	$ 265,021
Other comprehensive loss:
Foreign currency translation loss	(7,439)	(5,784)	(1,092)
Release of cumulative translation loss to earnings related to substantial liquidation of Discount Supplements	1,619	0	0
Other comprehensive loss	(5,820)	(5,784)	(1,092)
Comprehensive income	$ 213,479	$ 250,088	$ 263,929