Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of an accounting change	$ 149,794	$ (314)
Retained earnings | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of an accounting change	149,800
Accumulated other comprehensive income (loss), net of deferred income tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of an accounting change	(149,794)	$ 0
Accumulated other comprehensive income (loss), net of deferred income tax | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of an accounting change	$ (149,800)