Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Allowance for doubtful accounts receivable	$ 3,957	$ 2,957
Accumulated amortization of finite-lived intangible assets	$ 634,518	$ 536,929
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	201,849,586	193,104,452
Common stock, shares outstanding	200,276,386	191,531,574
Common stock, shares unvested	17,876	24,876
Treasury stock, shares	1,573,200	1,572,878
Class A Non-Voting Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	0	2,703,846
Common stock, shares outstanding	0	2,703,846