Stockholder's Equity - Quarterly (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	May 19, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity, Class of Stock [Line Items]
Preferred stock dividends declared				$ 5,094	$ 5,094
Convertible Preferred Stock, Shares Issued upon Conversion	38.0619
Convertible Preferred Stock, Threshold Percentage of Stock Price Trigger				150.00%
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period				12,133,276
Purchase of treasury stock, shares				1,160,308
Treasury stock, shares, end of period		14,092,732		14,092,732
Treasury stock, cost, beginning of period				$ 186,846
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions				8,544	11,433
Purchase of treasury stock, cost				16,762
Treasury stock, cost, end of period		$ 215,323		$ 215,323
Treasury stock, average cost per share, beginning of period, in dollars per share				$ 15.40
Purchase of treasury stock, average cost per share, in dollars per share				14.45
Treasury stock, average cost per share, end of period, in dollars per share		$ 15.28		$ 15.28
Treasury Stock
Treasury Stock, Shares [Roll Forward]
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions				578,673
Treasury stock shares received, other				220,475
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions				$ 8,544
Treasury stock received, value, other				$ 3,171
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions, Average Cost Per Share				$ 14.76
Treasury stock received, per share, other				$ 14.38
Call Option
Equity, Class of Stock [Line Items]
Option indexed to Issuer's Equity, Value	$ 15,900
Minimum
Equity, Class of Stock [Line Items]
Convertible Preferred Stock, Threshold Consecutive Trading Days				20 days
Minimum | Call Option
Equity, Class of Stock [Line Items]
Option Indexed to Issuer's Equity, Strike Price				$ 26.27
Maximum
Equity, Class of Stock [Line Items]
Convertible Preferred Stock, Threshold Consecutive Trading Days				30 days
Maximum | Call Option
Equity, Class of Stock [Line Items]
Option Indexed to Issuer's Equity, Strike Price				$ 33.54
Convertible Preferred Stock
Equity, Class of Stock [Line Items]
Preferred stock issuance, net of issuance costs, shares	120,750
Preferred Stock, Dividend Rate, Percentage				5.625%
Proceeds from Issuance of Preferred Stock, net of issuance costs					117,200
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs				$ 3,600
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Convertible Preferred Stock | Retained Earnings/(Accumulated deficit)
Equity, Class of Stock [Line Items]
Preferred stock dividends declared		$ 1,700	$ 1,700	$ 5,094	$ 5,094