Stockholders' Equity, Stock Repurchase Program, Dividends and Shelf Registration (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended				6 Months Ended
	Apr. 16, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	May 31, 2019	Dec. 31, 2018	Apr. 23, 2018
Stock Repurchase Program [Abstract]
Incremental Class A shares authorized to buyback (in shares)								1,212,759
Stock Repurchase [Abstract]
Percentage of reduction in shares outstanding	(4.20%)
Stock outstanding (in shares)	27,600,000	27,700,000	28,800,000			27,700,000			29,000,000
Dividends [Abstract]
Dividends declared (in dollars per share)		$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.04	$ 0.04
Shelf Registration [Abstract]
Maximum amount of debt and equity to be issued under shelf registration										$ 500
Class A [Member]
Stock Repurchase Program [Abstract]
Average price per share of repurchased shares (in dollars per share)	$ 21.00
Stock Repurchase [Abstract]
Stock repurchased (in shares)	1,200,000
Average price per share of repurchased shares (in dollars per share)	$ 21.00
Percentage of reduction in shares outstanding	(12.40%)
Stock outstanding (in shares)	8,600,000	8,719,209	9,800,000			8,719,209			9,957,301
Class A [Member] | Stock Repurchase Program [Member]
Stock Repurchase Program [Abstract]
Shares repurchased (in shares)		147,402
Average price per share of repurchased shares (in dollars per share)		$ 19.02
Share available under program to repurchase (in shares)		591,054				591,054
Stock Repurchase [Abstract]
Average price per share of repurchased shares (in dollars per share)		$ 19.02
Class B [Member]
Stock Repurchase [Abstract]
Stock outstanding (in shares)		19,024,117				19,024,117			19,024,240