Basis of Presentation and Significant Accounting Policies - ASU Adoptions (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification due to TCJA		$ 4,500
Adjustments to retained earnings	$ 471,178	419,403
ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustments to retained earnings		1,200
ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustments to retained earnings		(344)
Early Adoption | ASU 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustments to retained earnings		$ (3)
Net Interest Income | Revenue | Revenue concentration
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage	79.00%