Other Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Costs to obtain contracts	$ 169,266		$ 157,970
Accumulated amortization of costs to obtain contracts	(18,361)		(16,485)
Operating lease right-of-use assets	24,451		25,465
Other assets	46,179		27,804
Other assets, total	221,535		$ 194,754
Amortization cost	$ 1,900	$ 1,500