Condensed Consolidated Financial Statements - Recent Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Recent Accounting Pronouncements
Long-term deferred income taxes payable	$ 609,957			$ 609,957		$ 565,404
Diluted earnings per-share (in dollars per share)	$ 0.95		$ 0.77	$ 1.61	$ 1.29
Adjustment | Accounting Standards Update 2015-17
Recent Accounting Pronouncements
Deferred tax assets, current						(129,300)
Long-term deferred income taxes payable						$ (129,300)
Scenario, adjustment | Accounting Standards Update 2016-09
Recent Accounting Pronouncements
Income tax benefit		$ 3,000