Earnings Per Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Earnings Per Share [Abstract]
Net income (loss) available to common shareholders	$ 23,877		$ 19,882		$ 2,657		$ (145,666)		$ 1,780		$ 25,576		$ 14,097		$ 15,845		$ (99,250)		$ 57,298		$ 31,770
Weighted average common shares outstanding - Basic (in shares)																	39,244		38,655		38,207
Dilutive effect of stock-based awards (in shares)																	0		732		436
Weighted average common shares outstanding - Diluted (in shares)																	39,244		39,387		38,643
Earnings (loss) per common share - Basic (in dollars per share)	$ 0.61	[1]	$ 0.51	[1]	$ 0.07	[1]	$ (3.74)	[1]	$ 0.05	[1]	$ 0.66	[1]	$ 0.36	[1]	$ 0.41	[1]	$ (2.53)	[1]	$ 1.48	[1]	$ 0.83
Earnings (loss) per common share - Diluted (in dollars per share)	$ 0.60	[1]	$ 0.50	[1]	$ 0.07	[1]	$ (3.74)	[1]	$ 0.05	[1]	$ 0.65	[1]	$ 0.36	[1]	$ 0.40	[1]	$ (2.53)	[1]	$ 1.45	[1]	$ 0.82

[1] The sum of the quarterly EPS data presented in the table may not equal the annual results due to rounding and the impact of dilutive securities on the annual versus the quarterly EPS calculations.