Basis of Presentation and Significant Accounting Policies - Effects of Adopting Topic 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Balance Sheets
Other current assets	$ 247,175		$ 241,029	$ 232,027
Total current assets	2,943,484			2,249,128
Other assets	447,816		421,328	241,750
Total assets	19,941,928			18,691,457
Accounts payable and accrued expenses	686,612			719,257
Other current liabilities	144,965		143,699	159,914
Total current liabilities	1,246,475			1,242,734
Other liabilities	608,156		598,659	661,710
Total liabilities	12,801,377			11,841,667
Accumulated other comprehensive loss	(718,169)		(787,119)	(785,189)
Retained earnings	587,483		522,465	252,689
Total stockholders' equity	7,140,551			6,849,790
Total liabilities and stockholders' equity	19,941,928			$ 18,691,457
Statements of Operations
Revenue	1,215,877	$ 949,525
Sales and marketing	159,776	128,927
Total costs and operating expenses	990,002	782,312
Income from operations	225,875	167,213
Income before income taxes	79,653
Income tax expense	(16,759)	(13,393)
Net income	$ 62,894	$ 42,062
Basic EPS (in dollars per share)	$ 0.79	$ 0.58
Diluted EPS (in dollars per share)	$ 0.79	$ 0.57
Statements of Cash Flow
Income taxes, net	$ (15,381)	$ (20,637)
Other assets	(6,694)	47,132
Other liabilities	(16,973)	3,093
Net cash provided by operating activities	300,907	$ 247,371
Calculated under revenue guidance in effect before Topic 606 [Member]
Balance Sheets
Other current assets	237,633
Total current assets	2,933,942
Other assets	262,854
Total assets	19,747,424
Accounts payable and accrued expenses	685,580
Other current liabilities	159,003
Total current liabilities	1,259,481
Other liabilities	677,089
Total liabilities	12,883,316
Accumulated other comprehensive loss	(719,072)
Retained earnings	311,943
Total stockholders' equity	6,864,108
Total liabilities and stockholders' equity	19,747,424
Statements of Operations
Revenue	1,212,041
Sales and marketing	163,078
Total costs and operating expenses	993,304
Income from operations	218,737
Income before income taxes	72,515
Income tax expense	(15,385)
Net income	$ 57,130
Basic EPS (in dollars per share)	$ 0.72
Diluted EPS (in dollars per share)	$ 0.72
Statements of Cash Flow
Income taxes, net	$ (17,550)
Other assets	(1,238)
Other liabilities	(14,496)
Net cash provided by operating activities	300,907
ASU 2014-09 [Member] | Difference between revenue guidance in effect before and after Topic 606 [Member]
Balance Sheets
Other current assets	(9,542)		9,002
Total current assets	(9,542)
Other assets	(184,962)		179,578
Total assets	(194,504)
Accounts payable and accrued expenses	(1,032)
Other current liabilities	14,038		(16,215)
Total current liabilities	13,006
Other liabilities	68,933		(63,051)
Total liabilities	81,939
Accumulated other comprehensive loss	(903)		(1,930)
Retained earnings	(275,540)		$ 269,776
Total stockholders' equity	(276,443)
Total liabilities and stockholders' equity	(194,504)
Statements of Operations
Revenue	(3,836)
Sales and marketing	3,302
Total costs and operating expenses	3,302
Income from operations	(7,138)
Income before income taxes	(7,138)
Income tax expense	1,374
Net income	$ (5,764)
Basic EPS (in dollars per share)	$ (0.07)
Diluted EPS (in dollars per share)	$ (0.07)
Statements of Cash Flow
Income taxes, net	$ (2,169)
Other assets	5,456
Other liabilities	2,477
Net cash provided by operating activities	$ 0