Other Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Costs to obtain contracts	$ 183,870		$ 183,870		$ 157,970
Accumulated amortization of costs to obtain contracts	(20,376)		(20,376)		(16,485)
Operating lease right-of-use assets	21,620		21,620		25,465
Other assets	59,727		59,727		27,804
Other assets, total	244,841		244,841		$ 194,754
Amortization cost	$ 2,100	$ 1,600	$ 4,000	$ 3,100